I am trying to configure visual studio to enable me to step into the .net framework source code when I am debugging.
I have tried with both Visual Web-Developer-Express
Have you set up the environment to load the symbols (note: by default, the symbols are not set to load - have not checked VS 11, btw (will do so later)).
You can also check out this article for info on symbols. I will have to check if there is a manual download for symbols for .NET.
You can also set up source server manually to http://referencesource.microsoft.com/symbols. You cannot browse the reference source.