You need to use a second instance of VS.NET to debug the one that’s running the code.
Put your control on a from 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 of debugging Open your code file, set your breakpoint, and you’re debugging.
Posted by Shawn Burke of MSFT in microsoft.public.dotnet.framework.windowsforms.