I log this program and have been using it for awhile (donation sent) but since updating I'm having problems. Running Windows 10. All of a sudden I'm getting a TMPF28.tmp file and when I go to save the tag the program freezes up. Help
see e.g. this thread
So see which other program accesses the file that you currently treat with MP3tag and close it.
There is no other program using the file. That is the only program open.
A look at the task manager should show that there are numerous other programs running.
The tmp file is generated if the padding is not big enough but for some reason the original file gets blocked by the OS (something outside MP3tag's control) so that the tmp file could not be moved to the original file. It would be up to you to check your environment which other program/process blocks the original file.