There’s a thread going over at the Apple Discussion Board on this:
https://discussions.apple.com/thread.jspa?threadID=1712136&tstart=60
Am I correct in assuming you Sony HD Handycam records in the AVCHD codec?
Apparently something with the AVCHD transcoding to ProRes in FCP got damaged with the Mac OS X 10.5.5 and/or QuickTime 7.5.5 updates.
As far as we can tell, this issue affects only Mac Pros and the issue is not occuring in iMovie ’08 (which transcodes to the AIC codec). I’ve sent Apple’s FCP development team an e-mail. However, I’m stuck without being able to do anything with my footage from two cameras. I have yet to try FCP on my MacBook Pro, but I’ve heard it works.