ipod not syncing to itunes, says associated with a different itunes but it's not!

I have not plugged in my ipod for a long time, (I have only been using itunes on the computer) but I just tried to update it today but plugging it in. Used the same laptop and I assume the same itunes, but got the message that if I want to sync, I will have to erase my ipod because it is associated with a different itunes! I've been using the same itunes so I have no idea what's going on, but I don't want to lose my playlists on my ipod! Help!