You are not alone with this problem, I’m having the very same problems with the very same JVC deck and FCP 5.1.2, I have 3 FCP systems and I upgraded all to FCP 5.1.2 and now all systems are having the same problem since the upgrade. I got one system to work today but it only captures half of the clip, then it says “searching for media” in the capture window. Please let me know if you find any solution to this problem.