We've just implemented CSS Friendly Control Adapters. We are also using AJAX extensions.

The problem is GridViewAdapter and row's postback. Clicking on a row resuls in "Invalid postback or callback argument.  Event validation is enabled using <pages enableEventValidation="true"/> in configuration or <%@ Page EnableEventValidation="true" %> in a page.  For security purposes, this feature verifies that arguments to postback or callback events originate from the server control that originally rendered them.  If the data is valid and expected, use the ClientScriptManager.RegisterForEventValidation method in order to register the postback or callback data for validation." I suspect it’s due to there is no method defined, but I don't have any prove. Before we installed the adapter it worked fine. We were binding some java script on each row. First we thought it was something to to with that. But the error remains even after we disable OnRowDataBound.

Bug? Is there a simple way to solve this?

Can you post the callstack in the error message (from the browser window)? Also, can you post your markup (and maybe some code)?

I faced the similar problem with gridview having pagingandsortingcallback = true did not worked.

Then I placed the gridview in updatepanel of ajax extension, which is working fine and there is no need for pagingandsortingcallback to enable true.

You may use this to solve the problem.