Hi,
I am having this weird problem with my aspx page design page.
I inserted a panel in a cotentPlaceHolder, within there is a table.
on the design page I get the error "error creating control . unknown server tag 'telerik:RadTextBox'.
when i run this page to the browser it look fine.
This error usually happens when the project does not contain a reference
to the Telerik.Web.UI assembly, or the reference is broken. Please have a look into this documentation.
Also can you make sure that the tagprefix in the telerik control declaration and that of the control are same.