Unable to debug framework source code

Question

Hi,

I have following setup

*) Windows 7 64bit

*) .net 4.0.30319 RTMRel (as reported by vs 2010)

*) VS 2010 10.0.30319.1 RTMRel (as reported by vs 2010)

*) Following settings to enable framework source debugging

   -unchecked "Just My Code"

 -checked ".NET Framework source stepping"

-checked "source server support"

-checked "Microsoft Symbol Servers"

        -unchecked Source file version mismatch option in debugging->general

-visual studio hosting process disabled

and following code in test app

static void Main(string[] args)

        {

            string s = "foobar";

            int i = s.LastIndexOf('b');

        }

when I try to step into LastIndexOf, I get a page "No Source Available". I can see that whenever I run the app after clearing the cache, mscorlib.pdb file gets downloaded and vs 2010 shows symbol file loaded from the same location.

 

Is there any thing I am missing to enable source code debugging?

 

Thanks,

Rizwan