I also had this happen to me. It seems to be the firewire cable. I tired 6 different cables and the only one that worked was the one that came with the hvx200! it was very weird…
USB was a major pain the in but, although it still only took me about 1.5x real time to transfer, and that was with FCP trascoding the footage (macbook pro 2.4ghz ).
-Brandon