Recently I was trying to debugging Silverlight code in a server running Windows Server 2008 with Visual Studio 2008 Team Edition, but the debug stepping was not working and no break point will be hit.

I was searching all the net and finally found a link where it was informed that Visual Studio 2008 SP1 has issues in stepping into breakpoint when the code is debugged in Server Class Multi Core Processor or Multi Processor environment.

Solution:

1. Open Visual Studio but do not open any projects.
2. Start the Task Manager (Ctrl+Shift+Esc) and navigate to the “Processes” tab.
   Right-click on devenv.exe and select “Set Affinity…” (this option is only available on multi-processor or multi-core machines).
   Uncheck every CPU except one and click OK.

Open your project and debug as normal.

Workaround notes and limitations:

1. If you restart Visual Studio, you will have to repeat these steps.
2. If you are attaching to a process to debug, you should perform the above steps on your target process before attaching Visual Studio.  (If you are debugging foo.exe, change the affinity on foo.exe.)

More Information: http://social.msdn.microsoft.com/Forums/en-US/vsdebug/thread/f3fcb4fb-8a08-4fa0-8d58-9ed6f3eb1193