I'm sure this is all my fault, messing around with things in the middle of the night, but:
Whenever I insert a CD or DVD into the slot, or a floppy into the external drive, my iMac tells me to re-insert it. Once I do that everything's okay; it works.
[I've recently updated to 9.0.4 and DVD 2.2]
Would appreciate any suggestions.
Cheers, Marc.