Also having this problem. Final Cut is reporting that it might be a Blackmagic plugin issue. Currently have Decklink 7.3.2 installed, the latest, which is supposed to play nice with FCP 7 and the newest Quicktime. Haven’t tried downgrading the Decklink software yet, wanted to see if others were having the problem without Blackmagic first.
Micah, are you using Blackmagic as well?