I've got a C#
Unable to copy file "obj\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.
Well, I solved the problem myself - though I still have no clue why. I decided to isolate the problem by removing all files from the project, then re-adding them and determining that way which file was the source of my trouble. So, one by one I reintroduced files to the project, compiled & cleaned each step of the way... until... I added the last one...
... and everything still worked fine.
I did a compare to the source control of my original .csproj; no real differences. And even when I tried reverting to the previous version of the .csproj, it still worked.
Black magic. If it works, sometimes it's better not to ask why - just accept it and move on...
EDIT: The problem is a recurring one, and I believe I've isolated it to when I have the form designer open of an abstract/generic form at compile time.
Lesson learned: Make sure the Form Designer of any abstract or generic forms or controls is closed before you compile! If not, you have to close VS and reopen!