My first guess would be a software issue with iTunes.
That's why my first advice would be to check for updates for iTunes. If iTunes is uptodate:
Completely remove iTunes and its components from your computer, using http://support.apple.com/kb/ht1925 for windows XP or http://support.apple.com/kb/HT1923 for windows Vista or windows 7, and afterwards reinstalling iTunes and try again.
If you use Mac, simply download and install a fresh copy of iTunes, no need to remove anything.
Keep me posted about the outcome