Trying to use ajax.

Your error is probably becasue you don't have all the AJAX components installed correctly. Most likely the web.config file does not have the proper references to the AJAX libraries. Do a search for converting current .NET application to AJAX enabled application. It will give you the full instructions. Basically you are going to create a new web site using the AJAX enabled web site template. Then copy the web.config that is generated by that project and add those statements to your web.config. Again for the full instructions do a google search or I'm sure there is a post here that details that.