I ran into this, Dan. In fact, I’ve spoken to Apple about it, without much success. What I discovered is that if you have a deck or camera connected to your computer by firewire, you must shut it down, and turn off the firewire selections in your A/V settings in FCP. Then it works. I reported this problem on this forum a while back, but I guess not many people do audio-only capturing. The fact that you are having this problem confirms that this might be a bug. It might help if you would report this to Apple through the feedback link in FCP. It might re-inforce what I’ve been telling them.