I've been unable to copy my music from iTunes to the iPod. When I try, iTunes freezes for a moment and then gives a message saying that it couldn't copy due to an unknown error (-50). Once it gave a message saying there was an unknown error (-69).
I would first go through this article in full, which should resolve the issue:
iOS: Troubleshooting USB connection
If that doesn't work, this next article might be worth a shot:
iTunes displays -50 error message when syncing iPod on Windows XP
I know it says it is for Windows XP and you have 7, but it may be of some help.
Retrieving data ...