mp3tag on windows 7

I have MP3TAG on my old Windows XP computer with no problems, now I have a new computer with Windows 7. I have installed MP3TAG and after I changed the titles I can't finish it.

Win7 is much more sensitve in respect to access rights.
Check if the folders in which MP3tag stores the data are actually accessible by the account you use for running MP3tag.
Esp. if you migrated from an XP system you may have to claim ownership of the folders and files again.

See the FAQs for locations where MP3tag stores files:

See Microsoft's advice pages for that, e.g.
(although this actually about XP, it also applies to W7).