Could not load type 'System.Web.UI.ScriptReferenceBase' from assembly 'System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'.

Challenge

If you are getting following error:
Could not load type ‘System.Web.UI.ScriptReferenceBase’ from assembly ‘System.Web.Extensions, Version=3.5.0.0,
Culture=neutral, PublicKeyToken=31bf3856ad364e35′.
Then you are on the right article

Solution

It’s highly likely that you compiled your code using .NET 3.5 Service Pack 1 but deployed to a system that has .NET 3.5 without Service Pack 1.
ScriptReferenceBase is a new class for Service Pack 1, clearly a refactoring of ScriptReference to allow common code for the new CompositeScriptReference class. If you compile your code using SP1, you will include a reference to this class, which does not exist in .NET 3.5 pre-SP1. When the non-SP1 runtime tries to load the class, you will receive the exception above.
Solutions are:

• Compile using .NET 3.5 without SP1.

OR

• Install SP1 on the target system