Are you sure you have a 2G iPod? See:
A 2G can go to iOS 4.2.1 via iTunes directly if you have iTunes 10.X on your computer.
A 1G can go to 2.2 via iTunes amd 3.1.3 via the link proved already in this discussion.
This may indicate a hardware issue with your device. Follow Troubleshooting security software issues, and restore your device on a different known-good computer. If the errors persist on another computer, the device may need service.