If you have DiskWarrior, run it! That's saved my FW disk many times.
FW disks are very sensitive how you turn them off... and also if there's a bad firewire cable.
So get a new cable, run DiskWarrior, then always drag the harddisk icon in the trash before you turn off the external FW drive, then unhook the cables.
After I've did that myself I haven't had any problems at all.
Hope this helps!