After upgrading from Visual Studio 2008 beta 2 to the RTM I got the following error:
Could not load file or assembly ‘System.Data.DataSetExtensions, Version=188.8.131.52, Culture=neutral, PublicKeyToken=b77a5c561934e089’ or one of its dependencies. The system cannot find the file specified.
Solution: Daniel Moth already figured this out last year:
“The reason for this is that many of the pre-release Fx 3.5 assemblies did not have their version set to 3.5 yet (I covered that in this post), but now they do. So if you change the version from “2.0” to “3.5” in the web.config file your project will build fine again.”