I will describe exactly what I was doing:
I had a bunch of FLAC files loaded into MP3Tag, those files had two cover embedded so I proceeded to remove one. All the files didn't had the same covers as they were different albums so I had to select a few at a time. The error happened when I selected the last batch and proceeded to remove the cover and then, without MP3Tag finishing to remove as the progress window showed, I clicked on another track to deselected the ones that were selected at the time (the tracks where MP3Tag was working on).
This is what I got:
Mp3tagError.log (1.3 KB)
Apparently the files were successfully processed because they didn't had the cover I choose to remove, I don't know what the error did but as far as I know nothing bad happened to the files or metadata. I'm just reporting just in case.