So you ran a fair bunch of programs at the same time?! Have you taken care that none of these programs tried to access the files that you modified with MP3tag which might have lead to a deadlock?
Also, I would check the following: if Windows does not end gracefully, then this may find its root cause in faulty hardware - so, are your connected drives ok? A check with crystaldiskinfo for hovering sectors would be nice plus a check of the filesystem integrity with chkdsk.
Are the files OK? Have you checked them with MP3diags? see here for a link:
Does this happen always with the same file or does it happen randomly? Or: is it reproduceable at all or was it just a single incident?
As MP3tag usually runs ok, it is very likely that you observed something local and so we have to find out what that was. And that can only be done by you, locally.