element 'xxxx' is not a known element

[Stephen]

Hi,
I am using Visual Studio 2010 with Framework 4.0 and the Telerik.Web.UI and Telerik.Web.Design dlls are versioned at 2010.3.1317.40
I have been having problems adding a user web control to an aspx page via mark up and have been getting the error shown above.
The user control is one of a series of user controls some of which incorporate Telerik RadComboBox controls.  Any user control which does not have a Telerik RadComboBox control within it can be found and added to the page markup without the error occurring.

Markup page Inherits from:
ScottishParliament.QAndMSearchControls.QAndMSearch (with QAndMSearch being the name (and class) of the aspx page).
The Telerik.Web.UI Assembly is registered on the markup page using:
<%@ Register Assembly="Telerik.Web.UI" Namespace="Telerik>Web.UI" TagPrefix="telerik" %>

The aspx page references the Telerik assemblies Telerik.Web.Design and Telerik.Web.UI found by browsing.

Each control is Registered on the mark up page.  All (working and non-working) reside in the same child folder.  They are all assigned a tagPrefix of uc and a TagName matching their ControlName with Src pointing to the relative path of the ascx file involved.
Eg
<%@ Register TagPrefix="uc" TagName="MSPUC" Src="~/ChildUserControls/MSPUC.ascx" %>

I am trying to add the control to a asp:panel control using
<uc:MSPUC ID="MSPUC1" runat="server" />

There is a Script Manager in place at the head of the list of user controls as I am aware that the Telerik drop list requires one.  This is entered as:
<telerik:RadScriptManager ID="ScriptManager2" runat="server" EnableTheming="True" />

The aspx page written in c# is part of namespace ScottishParliament.QAndMSearchControls.
It has a 'using ScottishParliament.QAndMSearchControls.ChildUserControls;' statement at the top.

All user controls (those that use Telerik components and those that don't) all belong to namespace 'ScottishParliament.QAndMSearchControls.ChildUserControls.
The example control MSPUC does not work and has an ASP Label and ASP DropList as well as a Telerik RadComboBox.  These all appear on the Designer.cs page and can be referenced in the user control's own code page without problems.
The control's own Markup page registers the Telerik Web UI assembly in the same way as the aspx page.

I can't work out why there is a difference in behaviour from these controls and after some investigation found that removing the telerik component from the user control and re-building allowed me to add the control to the aspx mark up.
I had read from somewhere that it might be a trust issue resulting in the Telerik assemblies not being found?

Thanks for any help that can be provided in advance.

[Simon]

Hi Stephen,

In order to help you resolve this problem we will need more information about the WebResource requests on the page. Before proceeding any further I would like to ask you replace the RadScriptManager with a standard asp:ScriptManager to see whether it resolves the issue.

In any case, please either provide me with a live URL where I will be able to observe the issue myself or capture the traffic of the page with FiddlerCap, save the logs and then send them to me (via a support ticket mentioning this forum thread). The page should have the RSM on it.

Thank you in advance for your co-operation and understanding.

Best wishes,
Simon
the Telerik team