Unable to debug MVC source code in Visual Studio 2010

I'm trying to debug MVC source code in Visual Studio 2010 using the Microsoft Symbols Server. I've configured Debugging options as seen below:

and my project is targeting .NET Framework 4.0. (as said in Debug .NET Framework's source code only shows disassembly in Visual Studio 2010)

When I try to load the symbols of System.Web.MVC.dll, some window pops up saying that they're being loaded. But in the end, the Modules window says they couldn't be found, call stack lines are still grayed out and I only get code from disassembly window.

Anyone knows what is happening?

Microsoft has not provided symbols/source code for the entire .NET framework via their symbol server. However MVC is opened source so you can seperately download the MVC source from Microsoft: http://aspnet.codeplex.com/releases/view/58781