ReportViewer error on debugging

Question

I am working on some code a previous developer built at my company trying to add a ReportViewer to an ASP.NET C# page. When I begin debugging I get the following.

 Parser Error Message: The base class includes the field 'ReportViewer1', but its type 
(Microsoft.Reporting.WebForms.ReportViewer) is not compatible with the type of control 
(Microsoft.Reporting.WebForms.ReportViewer).

I read some articles suggesting my reference might be old. I am referencing Microsoft.ReportViewer.WebForms 9.0.0.0.

I have a ReportViewer in a different page, same project, that is working. When I change my reference to WebForms 10.0.0.0 it breaks with a similar message. In order to get it working again I have to change back to 9.0.0.0 and put back my web.config from before I made this change.

To get all ReportViewers to work do I need to be on 9.0.0.0 or 10.0.0.0 and do I need to make changes to the web.config?

Here are the two report viewers. I don't see anything pertinent that is different with them.

Working today under 9.0.0.0 in page1.aspx

<rsweb:ReportViewer ID="ReportViewer1" runat="server" Height="515px" ProcessingMode="Remote" Width="100%" Visible="false">
    <ServerReport ReportServerUrl="http://servername/reportserver" />
</rsweb:ReportViewer>

Not working under 9.0.0.0 or 10.0.0.0 in page2.aspx

<rsweb:ReportViewer ID="ReportViewer1" runat="server" Font-Names="Verdana" 
    Font-Size="8pt" ProcessingMode="Remote" 
    WaitMessageFont-Names="Verdana" WaitMessageFont-Size="14pt">
    <ServerReport ReportServerUrl="http://servername/reportserver" />       
</rsweb:ReportViewer>

Answer 1

I had to change in page2.aspx the following line

<%@ Register Assembly="Microsoft.ReportViewer.WebForms, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"
Namespace="Microsoft.Reporting.WebForms" TagPrefix="rsweb" %>

to

<%@ Register Assembly="Microsoft.ReportViewer.WebForms, Version=9.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"
Namespace="Microsoft.Reporting.WebForms" TagPrefix="rsweb" %>

I guess the lesson to be learned is keep all your versions the same number from the reference through the rest of your code including your web.config.

Answer 2

The correct way when using MS report view controls is to install the Nuget package

https://www.nuget.org/packages/Microsoft.Report.Viewer

Install-Package Microsoft.Report.Viewer

This way, you will get the latest dlls in your solution and you will ensure that it will work when you deploy it on production server.