Both of your computers think they "own" your iPod

Resolution

You can use your iPod with more than one computer. If your iPod is configured to be automatically updated when you connect to one of your computers, iTunes on another computer may also try to update it when it's connected.

This can happen with any iPod model if you use iTunes 4 and copy the iTunes 4 Music Library file from one computer to another. The solution is to recreate the iTunes 4 Music Library file on the other computer.