iTunes telling me to repeatedly authorize account to sync ipod

I moved my iTunes from my PC to my Mac, and everything works great, except when I tried to sync my iPod with my Mac; iTunes repeatedly tells me to authorize the account/device/whatever, and when I do, it confirms authorization...but when I try and sync it again, the same thing happens over and over and over. Anyone have a clue what to do? I"m tired of having to boot up my PC just to sync my iPod for two minutes. Thanks!!