Commented Issue: The Controls collection cannot be modified because the control contains code blocks (i.e. ). [16041]

I am suddenly getting the following error seemingly related to the current .net 3.5 Ajax control kit dll although it has been working ok since the last release. Anyone any ideas? Paul J. Weighell

Server Error in '/' Application.

The Controls collection cannot be modified because the control contains code blocks (i.e. <% ... %>).
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.Web.HttpException: The Controls collection cannot be modified because the control contains code blocks (i.e. <% ... %>).

Source Error:
An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:

[HttpException (0x80004005): The Controls collection cannot be modified because the control contains code blocks (i.e. <% ... %>).]
System.Web.UI.ControlCollection.Add(Control child) +2108047
AjaxControlToolkit.ScriptObjectBuilder.RegisterCssReferences(Control control) +654
AjaxControlToolkit.ExtenderControlBase.OnLoad(EventArgs e) +50
System.Web.UI.Control.LoadRecursive() +47
System.Web.UI.Control.LoadRecursive() +131
System.Web.UI.Control.LoadRecursive() +131
System.Web.UI.Control.LoadRecursive() +131
System.Web.UI.Control.LoadRecursive() +131
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1436


Version Information: Microsoft .NET Framework Version:2.0.50727.1433; ASP.NET Version:2.0.50727.1433
Comments: I'm using code like '<%=Request["userid"] %>' in javascript, but I'm not pass the querystring with url. By removing the code line it is perfect.