I just updated to iTunes 11.
Now I get this error:
Huh? Some Googling turns up people with this problem in iTunes 7 & 8. That was a while ago. They suggested various things, including rebuilding the library (which I am NOT going to do unless it's the only option).
However, my search prompted me to look in my iTunes folder. Yikes: Most of those temp files appeared on 11/18/12, so this must have been happening before today when I upgraded.
So, is there a good solution? Why might this happen? Is re-building the library the only way? I'd rather not lose my date-added and play-count data.