Kostadin,
I don't understand the purpose behind that attachment. I looked at the code and it is mostly identical to what I gave you. Did you attach the wrong zip file? The files in that zip are: Default.aspx, Default.aspx.cs, WebUserControl.ascx, and WebUserControl.ascx.cs.
Default.aspx is mainly identical to WebForm1.aspx that I provided. The only difference is that you didn't use a master page, and you entered script references into the RadScriptManager. Otherwise, everything else is the same.
Default.aspx.cs is identical to WebForm1.aspx.cs.
WebUserControl.ascx is identical to WebUserControl1.ascx, except for the name.
WebUserControl.ascx.cs is identical to WebUserControl1.ascx.cs except for the name.
The zip file as provided still reproduces the issue since it is the same code.
Thanks,
Tim
