"value cannot be null parameter name: key"

Question

I am getting a "yellow screen of death" when debugging a website I'm working on. The error message is "value cannot be null. Parameter name: key." I'm trying to bind a formview to the selected index of a gridview. Everything appears to bind correctly when I set breakpoints in my selectedindexchanged method, I can view values of my formview, but when I continue running it, I get the above error message. I've tried adding a datakeynames property to the formview and get the same error message. I've searched here and google and see some results, but none that seem to fix or relate to my issue.

Some code is below:

protected void GridView1_SelectedIndexChanged(object sender, EventArgs e)
{
    lblMessage.Text = "";
    cbCalled.Visible = true;
    cbError.Visible = true;
    cbVerbal.Visible = true;
    btnSubmit.Visible = true;
    FormView1.Visible = true;
    FormView1.DataBind();
    FormView fv1 = FormView1;
    Label PathCountLabel = (Label)fv1.FindControl("pathcountLabel");
    TextBox PathResult = (TextBox)fv1.FindControl("PathResultLabel");
    if ((PathCountLabel.Text != "1 of 1 biopsies") && (PathCountLabel.Text != "Only 1 Pathology Ordered"))
    {
        PathResult.BackColor = ColorTranslator.FromHtml("#FFFFAA");
    }
}

 <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" 
        Visible="False" DataKeyNames="PatientID" DataSourceID="SqlDataSource1" 
        onselectedindexchanged="GridView1_SelectedIndexChanged" AllowSorting="True" onsorting="GridView1_Sorting">
    <Columns>
        <asp:CommandField ShowSelectButton="True" />
        <asp:BoundField DataField="PatientID" HeaderText="Patient Id" SortExpression="PatientID" />
        <asp:BoundField DataField="LastName" HeaderText="Last Name" 
            SortExpression="LastName" />
        <asp:BoundField DataField="FirstName" HeaderText="First Name" 
            SortExpression="FirstName" />
        <asp:BoundField DataField="PathCount" HeaderText="Path Count" 
            SortExpression="PathCount" />
        <asp:BoundField DataField="DateOfService" DataFormatString="{0:d}" 
            HeaderText="Date of Service" SortExpression="DateOfService" />
    </Columns>
</asp:GridView>
    <asp:SqlDataSource ID="SqlDataSource1" runat="server" 
        ConnectionString="<%$ ConnectionStrings:PathologyConnectionString %>" 
        SelectCommand="SELECT * FROM [PatientDB]">
    </asp:SqlDataSource>
<br />
</div>
<div id="rightCol">
<asp:FormView ID="FormView1" runat="server" DataSourceID="SqlDataSource2" 
    Width="708px">
    <EditItemTemplate>
        LastName:
        <asp:TextBox ID="LastNameTextBox" runat="server" 
            Text='<%# Bind("LastName") %>' />
        <br />
        FirstName:
        <asp:TextBox ID="FirstNameTextBox" runat="server" 
            Text='<%# Bind("FirstName") %>' />
        <br />
        DOB:
        <asp:TextBox ID="DOBTextBox" runat="server" 
            Text='<%# Bind("DOB") %>' />
        <br />
        PhoneNumber:
        <asp:TextBox ID="PhoneNumberTextBox" runat="server" 
            Text='<%# Bind("PhoneNumber") %>' />
        <br />
        ChartNumber:
        <asp:TextBox ID="ChartNumberTextBox" runat="server" 
            Text='<%# Bind("ChartNumber") %>' />
        <br />
        AccountNumber:
        <asp:TextBox ID="AccountNumberTextBox" runat="server" 
            Text='<%# Bind("AccountNumber") %>' />
        <br />
        PathResult:
        <asp:TextBox ID="PathResultTextBox" runat="server" 
            Text='<%# Bind("PathResult") %>' />
        <br />
        PreviousVisitNote:
        <asp:TextBox ID="PreviousVisitNoteTextBox" runat="server" 
            Text='<%# Bind("PreviousVisitNote") %>' />
        <br />
        PathSlipNote:
        <asp:TextBox ID="PathSlipNoteTextBox" runat="server" 
            Text='<%# Bind("PathSlipNote") %>' />
        <br />
        PathSlipCheckboxes:
        <asp:TextBox ID="PathSlipCheckboxesTextBox" runat="server" 
            Text='<%# Bind("PathSlipCheckboxes") %>' />
        <br />
        <asp:LinkButton ID="UpdateButton" runat="server" CausesValidation="True" 
            CommandName="Update" Text="Update" />
        &nbsp;<asp:LinkButton ID="UpdateCancelButton" runat="server" 
            CausesValidation="False" CommandName="Cancel" Text="Cancel" />
    </EditItemTemplate>
    <InsertItemTemplate>
        LastName:
        <asp:TextBox ID="LastNameTextBox" runat="server" 
            Text='<%# Bind("LastName") %>' />
        <br />
        FirstName:
        <asp:TextBox ID="FirstNameTextBox" runat="server" 
            Text='<%# Bind("FirstName") %>' />
        <br />
        DOB:
        <asp:TextBox ID="DOBTextBox" runat="server" 
            Text='<%# Bind("DOB") %>' />
        <br />
        PhoneNumber:
        <asp:TextBox ID="PhoneNumberTextBox" runat="server" 
            Text='<%# Bind("PhoneNumber") %>' />
        <br />
        ChartNumber:
        <asp:TextBox ID="ChartNumberTextBox" runat="server" 
            Text='<%# Bind("ChartNumber") %>' />
        <br />
        AccountNumber:
        <asp:TextBox ID="AccountNumberTextBox" runat="server" 
            Text='<%# Bind("AccountNumber") %>' />
        <br />
        PathResult:
        <asp:TextBox ID="PathResultTextBox" runat="server" 
            Text='<%# Bind("PathResult") %>' />
        <br />
        PreviousVisitNote:
        <asp:TextBox ID="PreviousVisitNoteTextBox" runat="server" 
            Text='<%# Bind("PreviousVisitNote") %>' />
        <br />
        PathSlipNote:
        <asp:TextBox ID="PathSlipNoteTextBox" runat="server" 
            Text='<%# Bind("PathSlipNote") %>' />
        <br />
        PathSlipCheckboxes:
        <asp:TextBox ID="PathSlipCheckboxesTextBox" runat="server" 
            Text='<%# Bind("PathSlipCheckboxes") %>' />
        <br />
        <asp:LinkButton ID="InsertButton" runat="server" CausesValidation="True" 
            CommandName="Insert" Text="Insert" />
        &nbsp;<asp:LinkButton ID="InsertCancelButton" runat="server" 
            CausesValidation="False" CommandName="Cancel" Text="Cancel" />
    </InsertItemTemplate>
    <ItemTemplate>
        Last Name:
        <asp:Label ID="LastNameLabel" runat="server" Text='<%# Bind("LastName") %>' />
        &nbsp;&nbsp;&nbsp;&nbsp; First Name:
        <asp:Label ID="FirstNameLabel" runat="server" Text='<%# Bind("FirstName") %>' />
        &nbsp;&nbsp;&nbsp;&nbsp; DOB:
        <asp:Label ID="DOBLabel" runat="server" Text='<%# Bind("DOB") %>' />
        &nbsp;&nbsp;
        <br />
        <br />
        Phone Number:
        <asp:Label ID="PhoneNumberLabel" runat="server" 
            Text='<%# Bind("PhoneNumber") %>' />
        &nbsp;&nbsp;&nbsp;&nbsp; Chart Number:
        <asp:Label ID="ChartNumberLabel" runat="server" 
            Text='<%# Bind("ChartNumber") %>' />
        &nbsp;&nbsp;&nbsp; Account Number:
        <asp:Label ID="AccountNumberLabel" runat="server" 
            Text='<%# Bind("AccountNumber") %>' />
        <br />
        <br />
        Biopsy Location:
        <asp:Label ID="BiopsyLocationLabel" runat="server" Text='<%# Bind("BiopsyArea") %>'></asp:Label>
        <br />
        <br />
        Path Result:
        <br />
                    <asp:TextBox ID="PathResultLabel" runat="server" 
            Text='<%# Bind("PathResult") %>' ReadOnly="True" TextMode="MultiLine" Width="600" Height="250" />

        <br />
        <br />
        Previous Visit Note:<br />
        <asp:TextBox ID="PreviousVisitNoteLabel" runat="server" 
            Text='<%# Bind("PreviousVisitNote") %>' ReadOnly="True" TextMode="MultiLine" Width="600" Height="250" />
        <br />
        <br />
        Pathology Lab Note:<br />
        <asp:TextBox ID="txtPathNote" runat="server" 
            Text='<%# Bind("PathNote") %>' ReadOnly="True" TextMode="MultiLine" Width="600" Height="150" />
        <br />
        <br />
        Note to DA/DT:<br />
        <asp:TextBox ID="txtDADTNote" runat="server" 
            Text='<%# Bind("DADTNote") %>' ReadOnly="True" TextMode="MultiLine" Width="600" Height="150" />
        <br />
        <br />
        Path Slip Note:<br />
        <asp:Label ID="PathSlipNoteLabel" runat="server" 
            Text='<%# Bind("PathSlipNote") %>' />
        <br />
        <br />
        Path Slip Checkboxes:
        <br />
        <asp:Label ID="PathSlipCheckboxesLabel" runat="server" 
            Text='<%# Bind("PathSlipCheckboxes") %>' />
        <br />
        <br />
        Patient Message:<br />
        <ASPNetSpell:SpellTextBox ID="txtPatientMessage" runat="server" TextMode="MultiLine" 
    DictionaryLanguage="English (International), English (Medical)" Height="88px" 
    Width="597px" Text='<%# Bind("PatientMessage") %>' onKeyPress="return macro(event);"></ASPNetSpell:SpellTextBox>
    <br />
    <asp:Label ID="pathcountLabel" runat="server" Text = '<%# Bind("PathCount") %>' Visible="false"></asp:Label>
    </ItemTemplate>
</asp:FormView>
<asp:SqlDataSource ID="SqlDataSource2" runat="server" 
    ConnectionString="<%$ ConnectionStrings:PathologyConnectionString %>" 

    SelectCommand="SELECT [LastName], [FirstName], [DOB], [PhoneNumber], [ChartNumber], [AccountNumber], [PathResult], [PreviousVisitNote], [PathSlipNote], [PathSlipCheckboxes], [PathNote], [DADTNote], [BiopsyArea], [PatientMessage], [PathCount] FROM [PatientDB] WHERE ([PatientID] = @PatientID)">
    <SelectParameters>
        <asp:ControlParameter ControlID="GridView1" Name="PatientID" 
            PropertyName="SelectedValue" Type="Int32" />
    </SelectParameters>
</asp:SqlDataSource>

I've added the stack trace from the YSOD

Server Error in '/' Application.
--------------------------------------------------------------------------------


Value cannot be null.
Parameter name: key 
  Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

 Exception Details: System.ArgumentNullException: Value cannot be null.
Parameter name: key

Source Error: 


 An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.  

Stack Trace: 



[ArgumentNullException: Value cannot be null.
Parameter name: key]
   System.Collections.Generic.Dictionary`2.FindEntry(TKey key) +10627293
   System.Collections.Generic.Dictionary`2.TryGetValue(TKey key, TValue& value) +12
   Microsoft.VisualStudio.Web.PageInspector.Runtime.WebForms.SelectionMappingRenderTraceListener.GetLiteralTraceData(LiteralControl literal, TraceData& data) +97
   Microsoft.VisualStudio.Web.PageInspector.Runtime.WebForms.SelectionMappingRenderTraceListener.GetTraceData(Object renderedObject) +421
   Microsoft.VisualStudio.Web.PageInspector.Runtime.WebForms.SelectionMappingRenderTraceListener.EndRendering(TextWriter writer, Object renderedObject) +79
   System.Web.UI.RenderTraceListenerList.EndRendering(TextWriter writer, Object renderedObject) +58
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +142
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +128
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +8
   ASPNetSpell.SpellTextBox.Render(HtmlTextWriter writer) +6035
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +57
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +128
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +8
   System.Web.UI.WebControls.TableCell.RenderContents(HtmlTextWriter writer) +57
   System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter writer) +32
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +57
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +128
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +8
   System.Web.UI.WebControls.WebControl.RenderContents(HtmlTextWriter writer) +10
   System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter writer) +32
   System.Web.UI.WebControls.FormViewRow.Render(HtmlTextWriter writer) +38
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +57
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   System.Web.UI.WebControls.Table.RenderContents(HtmlTextWriter writer) +211
   System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter writer) +32
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +57
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +128
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +8
   System.Web.UI.WebControls.WebControl.RenderContents(HtmlTextWriter writer) +10
   System.Web.UI.WebControls.FormView.Render(HtmlTextWriter writer) +86
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +57
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +128
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +8
   System.Web.UI.Control.Render(HtmlTextWriter writer) +10
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +57
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +128
   System.Web.UI.HtmlControls.HtmlForm.RenderChildren(HtmlTextWriter writer) +102
   System.Web.UI.HtmlControls.HtmlContainerControl.Render(HtmlTextWriter writer) +32
   System.Web.UI.HtmlControls.HtmlForm.Render(HtmlTextWriter output) +53
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +57
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.HtmlControls.HtmlForm.RenderControl(HtmlTextWriter writer) +40
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +128
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +8
   System.Web.UI.Control.Render(HtmlTextWriter writer) +10
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +57
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +128
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +8
   System.Web.UI.Page.Render(HtmlTextWriter writer) +29
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +57
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1386




--------------------------------------------------------------------------------
Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.18446  

Answer 1

I tried everything you said and it didnt work. However, I found a workaround that, for some reason I dont know, worked. I added this to my web.config file:

 <add key="PageInspector:ServerCodeMappingSupport" value="Disabled" />

And it worked for me :D

Answer 2

This can be caused by browserlink in Visual Studio being enabled. Disable it:

http://www.asp.net/visual-studio/overview/2013/using-browser-link#disabling

Answer 3

Try closing the Visual Studio and and access the same page. It should work. I also faced the same exception. If you see the exception it points to PageInspector of Visual studio which causing the issue. Not sure why VS is messing with application loading.