I had the same problem with my shared files in docs and setts and it got so bad it kept freezing the computer. Anyway its got to do with the files you have downloaded. Go back to itunes get the error message and click on the details, now take note of the name and info on the file/s.
Then close it, go to start and click on search, then tye in the file and search your comp when you find it delete it...

you can always redownload it again later...

I hope this helps....let me know......