-10810 Finder error with FW 400 external drive

I have an external drive with USB 2 and FW 400 connections. For years I've used it without any problems with the USB connection. Recently I've connected it using FW 400 and have repeatedly had the following problem:

I am using files on an external drive (Mac OS Extended, Journaled) with a FW 400 connection when suddenly both the application I'm using and the Finder hang. I pick Force Quit from the Apple menu and in the list the app and the Finder both show up as not responding. I can force quit the app at that point but when I try to force relaunch the Finder it kills the finder rather than relaunching it. If I try to launch it from the Dock I get an error saying "The application Finder can't be opened -10810." After about 5 minutes I get an error message saying that I'd improperly disconnected my FW drive without ejecting it first (even though I neither ejected it nor disconnected it). At that point, the Finder relaunches and everything seems fine, though the FW drive (still plugged in and turned on) is now gone and doesn't appear in Disk Utility. If I unplug and turn off the FW drive and then plug it in again and turn it on again it will mount. Then the app that I was originally using relaunches on its own. At that point I can quit everything, eject everything, and restart without difficulty. Disk Utility finds nothing wrong with the external drive.

Any idea what's going on and how to fix it?

Obviously I could just go back to USB but I want to know what's going on.

Thanks!

Danny

MacBook 4,1

Mac OS X 10.6.8