On clean installation of Windows 10, mp3tag fails to start. I get an error window stating:
Server Busy
This action cannot be completed because the other program is busy. Choose "Switch to" to activate the busy program and correct the problem.
That is strange as I run it at the moment on W10 without any glitches.
Check if you have installed it under the same user id that runs it in the end.
Or, if you have a portable installation, check the access rights for the program folder.