I was trying to use ajax control toolkit in sharepoint 2010, but i get some errors. I found that the last release of the toolkit doesn\'t work with SP2010, so i downloaded t
Take a look at this blog article which explains how to use the Ajax Control Toolkit with SharePoint 2010 http://www.inspiredbytechnology.com/index.php/2010/10/28/using-the-ajax-control-toolkit-with-sharepoint-2010/
It looks like your web part references version 3.5.40412.0 of the AJAX Control Toolkit in an @Register directive. Since you want to use version 3.0.30930.28736, and since that version is properly referenced in your web.config, you should register the toolkit in your web part using its assembly name and namespace only, e.g.:
<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit"
TagPrefix="ajax" %>