itunes version 10.5 error message (-50)

I am getting an error message that says my itunes library cannot be saved . the error code is (-50). I recently updated to version 10.5. I tryed downloading a CD which workied fine, but kept getting message everytime a track downloaded. I tried playing the track after it was done, and it played fine. I logged out of itunes and then went back in, and could not find the new CD in my libaray. I am assuming it was saved to my external hard drive, but I cannot get rid of the error message. What should I do?