Unable to create type 'ajaxToolkit:ValidatorCalloutExtender'. Could not load file or assembly 'System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.
The reason of this error is because the application uses Microsoft ASP.NET 2.0 AJAX Extensions 1.0, but they had not been installed on the machine. You can download extensions here ASP.NET AJAX Downloads.
