Visual Studio user-mapped section open.

As one of the solutions I’m working is getting larger and larger (50+ projects), Visual Studio sometimes “forgets” to let go of its own handles: Unable to copy file “obj\Debug\YOURASSEMBLY.dll” to “bin\Debug\YOURASSEMBLY.dll”. The requested operation cannot be performed on a file with a user-mapped section open. I don’t know what a user-mapped section is to…