this error indicates a system exception, mostly these are illegal access errors. It may be a CloneDVD problem, but since there were no such reports before, I think that your system is somehow unstable.
Perhaps we can narrow this down:
Is it reproducible? Does it happen always with the same DVD at the same position, or is it appearing randomly?
You said 'at different parts of the rip', so I assume it happens randomly, correct me if I am wrong.
Is it more likely when you use a specific a different DVD title, source-drive or target-drive?
Is it more likely when your computer was running for a long time before starting CloneDVD?
Is it more likely at the end of a DVD, or at the beginning?
Is there other DVD-ralated software installed on your machine, which may interfere the reading/writing process?
BTW: If someone else is experiencing this problem, please report it here.