to debug asp.net mvc4

Go to Tools -> Options -> Debugger -> General

Uncheck the option Enable Just My Code (Managed Only)

Uncheck the option Enable. NET Framework source stepping (this is optional)

Check the option Enable source server support

Uncheck the option Require source files to exactly match the original version

symble servers:
http://referencesource.microsoft.com/symbols http://srv.symbolsource.org/pdb/Public http://srv.symbolsource.org/pdb/MyGet http://msdl.microsoft.com/download/symbols
to debug unity source code
http://unity.codeplex.com/releases/view/31277
download symbols:
http://unity.codeplex.com/downloads/get/467070
reference:
http://thechefprogrammer.blogspot.com/2013/04/debugging-into-aspnet-mvc-4-source-code.html http://stackoverflow.com/questions/13609891/how-to-step-into-mvc4-source-code-without-building-assembly