System.TypeLoadException: Could not load type 'System.ServiceModel.Activation.HttpModule' from assembly 'System.ServiceModel, Version=3.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'

System.TypeLoadException: Could not load type 'System.ServiceModel.Activation.HttpModule' from assembly 'System.ServiceModel, Version=3.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'

This started happening after I enabled WCF HTTP and Non-HTTP Activation under Micosoft .NET Framework 3.5.1.

Fix : - run ASP.Net regiis again from 4.0. (Run VS 2010 command prompt and execute aspnet_regiis -i).