I solved it. Appearently, we cannot use this control without ToolkitScriptManager
. But this doesn't solve the error.
There was some if conditions in <% %>
brackets in <head runat="server"> ... </head>
section, I had to remove them. And added Page.Header.DataBind();
to the page_load
to make it work.
This is how I added it to MasterPage. Hope it helps someone.