I was having the same problem, I had my Canon XH-A1 connected via FireWire to my Mac, and I was editing HDV 1080i60 video, I logged and captured video okay I did all the editing fine, until I tried to output my 30 sec commercial back to my XH-A1. After a lot of reading and testing, even tried a new FW cable.
This is it: Turn your camera on, put it on VCR, ( make sure the FW cable is unplug from the camera at
this time ) go to menu SIGNAL SETUP go to PLAYBACK STD enter and select DV, exit the menu and connect the FireWire cable, you should be back to normal. Go the to FCP and make sure audio and video settings are correct, remember to set to HD FIRE WIRE BASIC.
Good lock to all!