said by kitsune:
Is the VM on a separate partition? If not have you excluded it from your backup? If it's not on a separate partition or excluded then every time you open the VM it will trigger TM to backup all of it.
As a side note, if you just got 10.8 you have 90 days of support from Apple. So if all else fails you can call in to have them take a look at it.
No, the VM is on the same partition. I've not excluded it from my backup. But why should I have too? This wasn't an issue in 10.7.3. And it saved my hide a couple of times when I'd been lax in doing updates and got drive-by downloads. Just ask TM to put the VM back from 2 days ago.