-9136 Error when recording to ext. HD but not w/int. HD

[thelonious]

Mbox (original)
Pro Tools LE v7.3.1cs6
Mac PowerPC G4 PowerBook 500 MHz
1 GB SDRAM
OS X10.4.10
Digi CoreAudio Manager v7.3cs1
Glyph GT050Q External HD

Mbox Playback Engine Settings:
H/W Buffer Size: 1024 Samples
RTAS Processors: 1 Processor
CPU Usage Limit: 85%

DAE Playback Buffer: Level 2 (Default)

Tracks in use: 4
No Plug-Ins

the problem: -9136

Hi. When i attempt to record to my external Glyph FireWire HD, i get:

Error Message: CPU usage is holding off USB audio. Remove some Plug-Ins, delete some tracks, or increase the "H/W Buffer Size" in the Playback Engine dialog. (-9136)

But when i record to my Mac HD with the same configuration, the error doesn’t occur and recording goes smoothly.

(I’ve also been getting noise bursts and white noise while using Digi CoreAudio Mgr., so I installed Mbox Firmware v22 yesterday. Hope it’ll stop the shocking noise bursts!)

What can I do to resolve the 9136 error and enable recording to my Glyph Ext. HD?

Thank you.

[The Dougfather]

Mac PowerPC G4 PowerBook 500 MHz

The minimum recommended processor for Pro tools 7 is 1Ghz, have you had success with earlier versions of 7 on this machine?

Cheers

[thelonious]

i recently upgraded from v6 to 7.