Unable to debug in VS2010

I was getting following message while running my VS2010 in debug mode:

"Unable to automatically step into the server. Unable to determine a stopping location. Verify symbols are loaded. Symbol not found: Service.HelloWorld()."

While doing more investigation I did find that my Visual studio was unable to attach to the aspnet_wp.exe when I hit
the start debug button. After doing some reserach I was able to find the issue. My webservice was upgraded to use .Net 4.0 but WPF code was still using .NET 3.5. After changing my WPF to .NET 4.0 issue was fixed.

you can look at other articles also:

Debug ASP.net web services http://msdn.microsoft.com/en-us/library/aa291236(VS.71).aspx

Enable debugging for ASP.NET application http://msdn.microsoft.com/en-us/library/e8z01xdh