Imovie Export to Camera Problem - Ext Hd?


I have a G4 Powerbook set up to do video via firewire using Imovie and a WEstern Digital external hd. Cabling is daisy chain...laptop to HD and HD to camera. All works well getting video from camera into Imovie. Then I'd like to export back to camera but can't. "Export to Camera" seems to be goes into record mode and tape starts, but nothing is recorded. a test, I found that I CAN EXPORT a movie directly from my laptop, disconnecting the ext hd and going directly from laptop to camera, again via firewire. I've tried different cameras, different cables, always the same result. So ....I'm wondering if there's an issue with Western Digital HDs and Imovie?
any thoughts would be great. thanks,
My guess would be some kind of opposite direction throughput problem with the firewire chip set in the external drive.