I actually encountered something quite similar a while ago. I updated my XMPlay by copying the contents of the zip to my XMPlay folder, which was named XMPlay 2.6 at the time. There was no problems in doing this, but when I then tried to rename the folder to 2.7, it said like "cannot rename folder, because file is in use" or so. Here too: no it wasn't.
So I tried to track down the file causing problems, and surprisingly it wasn't xmplay.exe. I found out, that it was in "skins"-folder, by attempting to rename the folder, which couldn't be done. Then I tried to rename the individual files there, but they all could be renamed fine.
So finally I just ended up restarting my comp, and as expected, now I was able to rename it at last. I have no idea, what could it be with that folder. I renamed every file there, and I also have set it so, that all hidden and system files are shown too. Go figure

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