I had similar issues with my lightbridge. Here's a few things to try.
First, Do Not install the Beta drivers (1.8.3.x) . If you have, Uninstall them. I couldn't get it to work at all, especially if it needed to sync.
Download the 1.8.2 drivers from M-Audio. Power off and unplug the lightbridge. Install the drivers, then shutdown the computer. Connect the lightbridge and power it up, then power up the mac. I'm running OS X 10.5.2 on a macbook pro, and once I went back to the 1.8.2 drivers, everything worked again.
Also, I find the lightbridge to be very touchy if other Firwire Devices are running, especially audio interfaces. My advice, be sure that the only FW device plugged in is the Lightbridge. You might get away with a drive if you need it, but I tend to turn mine off.