A: There are several ways to check which process has a file locked, including solutions from SysInternals, but another utility was brought to my attention that has a very simple interface. It's focused just on finding the process locking a file.
EMCO UnLock IT can be downloaded for free, and once it's installed, just browse to the file that's locked. UnLock IT shows the process that has the file locked and gives you an Unlock Resource button.
You should obviously be careful when unlocking resources, because locks are often there for good reasons, to protect a file from corruption or because the file is being used by multiple processes. However, if you have a problem with a stuck, locked resource this is an easy way to resolve it.