Sounds like the file header needs to be compressed to allow progressive downloading. Open the file in QT and save it with a new name to compress the file header.
The only other thing is to make sure you have a high-quality RS-422 cable. Try another cable if you have it. I’m using a Comprehensive RS-422 cable. Also make sure the “use deck search mechanism” is checked. You might also try to make a new device preset from scratch using the Panasonic RS-422 protocol. If I think of anything else, I’ll let you know.
Apple changed the RS-422 polling interval from FCP 4.5 to version 5.0. This seems to cause trouble in “older” Panasonic decks. AJA released a plug-in that slows down the polling interval in FCP 5. It works great. Email me if you’d like me to send it to you. john_kaley (at) mac (dot) com