Mac mini won't run DVD player even though Superdrive is attached

When we attempt to play a DVD on our new Mac mini with the (MacBook Air) Superdrive attached, we get the following error message:

"There was an initialization error
A valid DVD drive could not be found [-70012]"

We're puzzled because the drive does play CDs, and the DVDs we put into it show up on the desktop. Furthermore, System Information (the new System Profiler) says "Reads DVDs -- YES."

What is going on? We've read about other people getting this message when a disk is stuck in the drive and/or won't show up on the desktop, but in this case the disk seems fine but it just seems that DVD player doesn't quite trust it.

Any ideas?

Thanks in advance,

JD