I have a 3000-file library combination wma and mp3. With 2.48 on Windows 7 64-bit, I fairly often get this error:
'File "filename.mp3" cannot be opened for writing.'
There is a thread on this issue having to do with network drives, but for me there is no network element. This happens on my C: drive.
I never used to get this error, but I only recently began using mp3tag again, after a long absence (I can't remember the version I was using just prior to 2.48).
So far, this error is just annoying, as the file being edited -does- edit successfully. I haven't been able to discern a pattern, but it happens maybe ~ 10-15% of the time, especially when marking several files for editing. mp3tag will say it saved the tags in all but one file, for example (but it actually also saved the tag in that file as well).