When moving or deleting a file or a folder, I sometimes get error saying that the file is being used by another process. If that happens, I need to use external tool to see what processes are using the file. Sometimes I have already closed the lister, so I have to open it back, find the problematic file and use e.g. LockHunter to see what process use it.
How about having DOpus display a list of processes that use the file?
Opus does this already when deleting, as long as you don't use the recycle bin. (Deleting to the Recycle Bin is handled by Windows, and largely outside our control.)
(It also depends on a Windows API to get the list of programs locking the file, and that API misses some cases. I think some lock-detection tools use another method which involves injecting code into every process, which wouldn't be suitable as something that happened automatically.)
Doing it when moving as well isn't a bad idea.