Element 'RadGrid' is not a known element

Question

I'm trying to use the Telerik RadGrid, but I'm getting the following warning:

"Element 'RadGrid' is not a known element. This can occur if there is a compilation error in the Web site, or the web.config file is missing."

Here are some things that I've already checked:

• The web.config file isn't missing, and there aren't any other compilation problems on the page.
• The Telerik.Web.UI dll is in the GAC, and the project's references point to that file. No Telerik dlls in the bin folder.
• The assembly is added in the web.config using this in the assemblies section: <add assembly="Telerik.Web.UI, Version=2011.1.413.35, Culture=neutral, PublicKeyToken=121fae78165ba3d4"/>
• The properties of the RadGrid work, so Visual Studio is able to figure out what the object is
• The page runs normally, I just have this annoying set of warnings.
• I tried adding an @Register statement for the Telerik assembly on the page, but got no change
• I tried clean/rebuild, but no change
• I tried restarting Visual Studio, no change
• I tried restarting the machine, no change

EDIT: Here's the markup I'm using.

<%@ Page Title="" Language="C#" MasterPageFile="~/masterPages/ActionAreaSinglePanelMaster.Master" AutoEventWireup="true" CodeBehind="overview.aspx.cs" Inherits="Compass.overview" %>


<asp:Content ID="PanelHeaderContent" ContentPlaceHolderID="PanelHeaderPlaceholder" runat="server">
    <p>Panel header</p>
</asp:Content>


<asp:Content ID="PanelContent" ContentPlaceHolderID="PanelDataPlaceholder" runat="server">
    <asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager>
    <script src="../Scripts/jquery-1.4.1.js" type="text/javascript"></script>
    <script src="../Scripts/radGridLayout.js" type="text/javascript"></script>
    <script type="text/javascript">
        panelGridID = "<%=panelGrid.ClientID %>";
    </script>

    <asp:ObjectDataSource ID="BundleItemsSource" runat="server" TypeName="Compass.Data.CompassUI" SelectMethod="BundleDataSet">
        <SelectParameters>
            <asp:QueryStringParameter Name="bundleID" QueryStringField="bundle" />
        </SelectParameters>
    </asp:ObjectDataSource>

    <telerik:RadGrid id="panelGrid" runat="server" DataSourceID="BundleItemsSource" Height="100%" Width="100%">
        <ClientSettings>
            <Scrolling AllowScroll="True" UseStaticHeaders="True" />
            <ClientEvents OnGridCreated="gridCreated" />
        </ClientSettings>
    </telerik:RadGrid>

</asp:Content>

Answer 1

Close Visual Studio, delete the schema cache, and re-open Visual Studio. You can find the schemas under something like:

C:\Users\karthik\AppData\Roaming\Microsoft\VisualStudio\10.0\ReflectedSchemas

It is safe to delete all files in this folder.

Answer 2

Changing the Assembly attribute to remove the specific version, public key, etc apparently fixed the problems.