You need to use a second instance of VS.NET to debug the one that’s running
Put your control on a form in VS.NET
Start a 2nd Vs.Net
Choose the Debug menu >> Processes …
Double click ‘devenv.exe’ and choose ‘Common Language Runtime’ as the types
Open your code file, set your breakpoint, and you’re debugging.
Posted by Shawn Burke of MSFT in microsoft.public.dotnet.framework.windowsforms.