IIS Error : 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.

Error

Some times we face Application error in "/" application after migration the ASP.net site from one server to other ever after making all the changes perfect.

Error :  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.

Resolution:

1. Check if you application folder contains a folder with name "ajax" when you copied it from old server.

2. If yes then download and install the Ajax Extensions 1.0 for ASP.NET 2.0 on new server.

3. Reset the IIS (though it is not necessary but its good to reset IIS after such installation.)

You can download Ajax Extensions 1.0 from from Microsoft Download Center.

Solution Applies to:

Windows Server 2003. IIS 6.0, ASP.Net 2.0