When doing WinForms development in Visual Studio 2010 (including SP1), be aware of a bug with UserControls that hamper debugging; sometimes you get an error like this:
Error 9 Unable to copy file "obj\x86\Debug\MyProject.exe" to "bin\Debug\MyProject.exe". The process cannot access the file 'bin\Debug\MyProject.exe' because it is being used by another process.
When using SysInternals’ Process Explorer to see which process has handles open to MyProject, you will see that devenv.exe (The Visual Studio IDE) is the culprit: sometimes it has a lot of handles open.
The workaround is simple: close all UserControls before debugging your WinForms application.
A real pity, as UserControls are a very useful feature when developing software (many platforms use the same paradigm, .NET certainly wasn’t the first to introduce it, and it is available in for instance WPF as well).
Note that there are other causes of the same error message, but for me this was the issue.
–jeroen
The Wiert Corner - irregular stream of stuff 