Consider this common construct that you and I have thrown into ASPX pages for years now:
<%# DataBinder.Eval (Container.DataItem, "EmployeeID") %>
In .NET 3.5.1 and older it returns -- tada -- a string. No mystery there. But in .NET 4.0 it returns the same type as the underlying data type -- which in this case for me was a nullable int. Interesting, no?
The GAC in .NET 4.0 is cut into two parts now -- one half for .NET Framework 2.0 stuff, and the other for v4.0 stuff. When compiling any project, targeting .NET 2.0, 3.5, or what have you, this annoying error may pop up: Could not load file or assembly 'System.EnterpriseServices, Version=184.108.40.206, Culture=neutral, PublicKeyToken=b03f5f7f11d5... or one of its dependencies. The system cannot find the file specified. If you are working on a 32-bit system then open a run box and perform this copy command: ......