OK, I wanted to add some things I found out. The computer in question is an HP laptop with a fresh full Windows 8 install (not an upgrade install).
The laptop has a built-in optical drive D:, but that drive has had problems so I purchased an external USB DVD writer, which is E:.
In my first post, when I put an audio CD in the external drive E:, I get an error.
So, I put an audio CD in D: (internal drive) and it plays fine.
If I have an audio CD in D: (internal drive) and put an audio CD in E: (external drive) and ask MC18 to play the audio CD in E:, it plays the corresponding track on D: but reports it is playing E:. So, if no disc is in D: it reports an error.
Note that WMP plays these scenarios correctly. You can switch back and forth between D: and E: at will and play both successfully.
It appears MC18 may be confused about playing my second external drive. It thinks its playing the 2nd external drive but it actually playing the internal drive.