Error when I try to launch website in IIS: Value cannot be null. Parameter name: key

Question

I try to launch a website in IIS and get this error. I don't know what's the reason of it, because this site was created by another person, not me.

Stack trace:

`System.Collections.Generic.Dictionary`2.FindEntry(TKey key) +14370237
   System.Collections.Generic.Dictionary`2.TryGetValue(TKey key, TValue& value) +20
   Microsoft.VisualStudio.Web.PageInspector.Runtime.WebForms.SelectionMappingRenderTraceListener.GetLiteralTraceData(LiteralControl literal, TraceData& data) +71
   Microsoft.VisualStudio.Web.PageInspector.Runtime.WebForms.SelectionMappingRenderTraceListener.GetTraceData(Object renderedObject) +220
   Microsoft.VisualStudio.Web.PageInspector.Runtime.WebForms.SelectionMappingRenderTraceListener.EndRendering(TextWriter writer, Object renderedObject) +47
   System.Web.UI.RenderTraceListenerList.EndRendering(TextWriter writer, Object renderedObject) +90
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +12372803
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +246
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +150
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +246
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +150
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +246
   System.Web.UI.UpdatePanel.RenderChildren(HtmlTextWriter writer) +331
   System.Web.UI.UpdatePanel.Render(HtmlTextWriter writer) +114
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +150
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +246
   System.Web.UI.HtmlControls.HtmlForm.RenderChildren(HtmlTextWriter writer) +151
   System.Web.UI.HtmlControls.HtmlContainerControl.Render(HtmlTextWriter writer) +49
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +150
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +246
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +150
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +246
   System.Web.UI.Page.Render(HtmlTextWriter writer) +40
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +150
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +5363`

Answer 1

The PageInspector normally acts up if your server controls are out of date or are older versions. If you're using external ASP.NET Server controls, try to upgrade them.

And if a workaround is fine for you, then you can disable page inspector as follows:

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