InvalidCastException whilst grouping on the RadGrid

[Gordon]

I have a radgrid which works really well.  I've extended the functionality to use grouping, but whenever a column is dragged to the grouping area, or dragged from the grouping area back to the columns; an InvalidCastException occurs.

[InvalidCastException: Unable to cast object of type 'Telerik.Web.UI.RadGrid' to type 'Telerik.Web.UI.GridTableView'.]
   Telerik.Web.UI.RadGrid.RaisePostBackEvent(String eventArgument) +1692
   System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +13
   System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +175
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1565

I've checked my httphandlers section in the webconfig (as a previous thread suggests), but the relevant Telerik.Web.UI.WebResource.axd entry is already present.

<httpHandlers>
      <remove verb="*" path="*.asmx" />
      <add verb="*" path="*.asmx" validate="false" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
      <add verb="*" path="*_AppService.axd" validate="false" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
      <add verb="GET,HEAD" path="ScriptResource.axd" type="System.Web.Handlers.ScriptResourceHandler, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" validate="false" />
      <add path="Telerik.Web.UI.WebResource.axd" type="Telerik.Web.UI.WebResource" verb="*" validate="false" />
    </httpHandlers>
    <httpModules>
      <add name="ScriptModule" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
    </httpModules>

Any ideas?

[Yavor]

Hi Gordon,

Can you please also provide the declaration of the control, as well as the code-behind file, so that I can try and recreate the setup locally?

Best wishes,
Yavor
the Telerik team

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[Gordon]

I've sorted the problem.

It was down to a stray key in the web.config

<xhtmlConformance mode="Legacy"/>

After finding the problem key, i googled it and found this helpful blog;
http://weblogs.asp.net/scottgu/archive/2006/12/10/gotcha-don-t-use-xhtmlconformance-mode-legacy-with-asp-net-ajax.aspx