Avid Pro Audio Community - DAE Error -9126, but seems I'm set up the right way

Hey guys,

I'm hoping to get some help here. I have read through countless threads dealing with dae error -9126, however none of the fixes are working for me.

I am running a 003 with Pro Tools 9.0.6 on a MacBook Pro, OSX 10.6.8 with an Intel Core i7, 2.66Ghz, 8GB memory. I have recently purchased an OWC Mercury Elite Pro (4TB) external hard drive to be dedicated to audio recording and playback. When I copy my sessions onto the external, they won't open and give me the -9126 error, however they open from my OS drive fine. When I start a new session on the external, I am unable to add or record audio to it, with the message "can not allocate space", however it works fine on my OS drive.

Digidesign recommends that the drive is formatted Mac OS Extended (Journaled) with Apple Partition Map- and never to use the GUID Partition Table. Got that, check- all seems to be what it is supposed to be. Besides this, the rest of my system is optimized as is recommended. The funny thing is that when I change the external to GUID (just for a test), all seems to work fine. No errors whatsoever.

I've gone through all the threads here and also have done all the regular troubleshooting, trashing prefs, plug-in compatibility and all of it. The only thing I can think of is that my OS drive has a GUID Partition Table, which I didn't think mattered. Does the OS drive need to be APM as well? That would be a real pain in the ass- really hoping that's not it.

I've also got my 003 chained at the end, through the external drive. All cables at a good short length. Here is how I'm set up:
MacBook Pro > FW800 > OWC HD > FW800/400 > 003

Any help is much appreciated!