Error Message -20 during iPhone 3G Backup

I'm trying to update to 4.0.1 from 4.0 on my iPhone 3G. To complete the update, a backup is required. I get an error message when I attempt to backup (either manually or when trying to initiate the update) that states:

iTunes could not back up the iPhone (iPhone name) because an unknown error occurred. (-20)

I have been unable to find any information regarding this specific error message.

I am on a Mac, running 10.6.4, and have only encountered this issue after updating to 9.2.1. I'm not sure if the issue is related to the iTunes update.

I have:

-uninstalled/reinstalled iTunes (discovered that the iTunes Helper was missing during uninstall)

-attempted on different USB ports on computer (directly connected, no USB hub)

The device is (obviously) recognized by the computer, and can sync content to iPhoto without issue. I am set to automatic sync, and have reservations about attempting to update from another machine.

Any assistance would be greatly appreciated.

Thanks!

-S.