I had added HTML extender to the form and it was working fine. Now when I try to add confirmbutton extender it gives me an error saying "unknown server tag ....". When I remove the confirmbutton extender it is fine. Can it be cached? Also now I don't see it in my AjaxTookKit either. I changed from scriptmanager to ajaxToolkit:ToolkitScriptManager in the master file. I added the following in aspx page.
<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit.HTMLEditor" TagPrefix="HTMLEditor" %>
I have the following in config file.
<add tagPrefix="ajaxToolkit" assembly="AjaxControlToolkit" namespace="AjaxControlToolkit" />