Firewire issues

I am experiencing significant issues with a couple of my firewire 800 drives and FCPX. I have not been able to locate the issue on my own and I need some help! Here's what happening...

With one of 4 different branded firewire drives (2 of which are brand new) connected to either my 15" 2009 MBP running Mtn Lion, loaded with RAM and using the discreet graphics card, or my 17" 2010 MBP with basically the same specs and running FCPX 10.0.08, I get a nasty crash whenever I attempt to render or export (Share) from FCPX. When I start a render it will begin the render and then just quit. I do not get any notice that anything is wrong except that the progress on the render stops. I have left it rendering for 8 hours or more just to see if it was a momentary hiccup. It was not. When this happens I have to Force Quit FCPX, then do a hard reboot on the computer before I can do anything else. It seems that when it locks up the firewire drive remains attached to FCPX so the computer will not shut down because even though I have force quit FCPX it has not released the drive.

Here is what I have tried...

1. Repairing permissions - had no effect
2. Trashed Prefs - nothing
3. Used Digital Rebellions tools - no effect
4. connected one of the FW drives via eSata - worked perfectly!
5. Duplicated one of the offending projects from the FW drive to the boot drive - everything worked perfectly
6. Tried different FW cables - no effect

I'm not sure what else to do, since this happens with different drives, different projects and different computers I am thinking that there is something going on with FCPX but I just cannot be sure.

Has anyone else seen this behavior? Any other troubleshooting ideas?

Thanks
Ken

Because No 5. worked, I'll bet it is the render files. Chose File > Remove Event/Project Render Files. Then choose to remove them all.