Could not load file or assembly ‘System.Web.Extensions, Version=1.0.61025.0, Culture=neutra...


This article is to resolve the error “Could not load file or assembly ‘System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35′ or one of its dependencies.”

If you ASP.NET solution is still based on .NET Framework 2.0 and you have the following line in Web.config.

<addassembly=“System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35“/>

In this case I might get the above mentioned error when you run your project.

What you need to do is download the Ajax installer from, install it, and run again.

Don’t waste your time to just copy the AjaxControlToolkit.dll into the bin folder without running the installation. It will be completely useless.