I am getting this error when I run the web application

I am getting error when I run the application,

Could not load file or assembly 'System.Web.Exten开发者_StackOverflow中文版sions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.

This is the error I am getting when I run the application, I added the new dll and increased the trust level. Can you help me please.

This you try to load on web.config on assembly session is too old (version 1)

Just remove the line from web.config and all is ok, you probably have the Extension again on assembly session from newer version net.

<add assembly="System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>