I am using FCP 5 and a GL-1 as well as a Panasonic cheapy (PV-GS-19). I have the same problems with both cameras. Today I had to use imovie to export my final video. My own workaround has been to unplug and then plug back in the firewire in both the computer and the camera. It works sometimes, pretty chincy though.
You may want to mention your camera, if you’ve tried Edit to Tape, Print to Video, and a straight from timeline playback. Also, are you able to log and capture?