Try using an earlier version of DVD2AVI - that same error often came up for me too, and it was DVD2AVI causing the problem. Othertimes, rebooting (!) solved it.
BTW, everyone - try MPEG Mediator. Really good piece of freeware. It's replaced DVD2AVI and VirtualDub for me, and also taken my encoding speed up from 20fps to 25fps... HIGHLY recommended.
Download:
http://www.mpeg-mediator.com/ - Original
http://www.wolf-town.com/modules/mydown ... ?op=&cid=4 - Special Edition! (recommended)