Sorry to bump this thread up but I have a fix that may help people getting the dreaded "data type is not supported" message for a chunk of their mp3 collection.
I have found that either of these solutions work:-
Using iTunes to fix the tags (please note I have not looked in depth to see if some ID tag data is lost by following this process so proceed at your own risk. This also looses the artwork but it can be retrieved again using iTunes however, after doing this it failed to display on the PS3 for some reason, even though it was present in iTunes. I can say that basic track, artist, album data is not lost:-
Highlight the single mp3 or your whole collection
Right Click to convert ID3 tags
Tick the box to change the version and choose v1.1
Click OK
Tell iTunes to re-fetch the art work as it disappears
Optionally - you can now convert the mp3 id tag version back up to 2.4 if you wish or just leave it at 1.1
OR
Download and run the open source MP3VAL and scan and then fix the mp3 or your whole collection. Note that on some errors that it finds in the scan, it warns that the sound quality could be degraded by the fix but on the test samples I ran it over I could not hear any difference. Also note that if you dont tick in preferences to delete backup files, you will end up with the mp3's duplicated as .bak files.
MP3val | Reviews for MP3val at SourceForge.net
Both options sorted the problems for me.
I hope this helps. It was driving me mad!