Must be some file missing somewhere. I never tried it (didn't think of it) but I wonder if a re-install of the same build from the same partition would solve that problem.

I'll have to try it next time it happens.

I don't think it's a UUID problem as I checked.

Shooting in the dark here.

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Gigabyte EX58-UD5 - i7 920 @ 3.2 GHx - eVGA 8800GT
Asus P5Q Deluxe - E8400 @ 3.6 GHz - Asus 7900GT
iMac 2.2 GHz - 4 MB