Pro Tools 8 wont play back my guitar recordings all of a sudden.

[funkyfresh]

I keep getting the message "The audio device buffer underflowed. If this occurs frequently, try decreasing the 'H/W Buffer Size' in the playback engine panel or remove other devices from the audio firewire bus. (-6805)"

I am very new to pro tools and I am not at all computer savvy. I have a brand new macbook pro leopard(which exceeds requirements for memory, processing speed, sound, etc. and has been working greatly for the last couple months) and I have the ProTools 8 Mbox 2. I have never had any problems with it and it was playing back just fine the same session I was recording. Nothing in digidesigns troubleshooting page or in the manual covers this and I can't find any answers that actually help. somebody said delete digidesign database folders.... i did that. another answer said mess with the sample rate... i did that.

Model Name: MacBook Pro
Model Identifier: MacBookPro5,1
Processor Name: Intel Core 2 Duo
Processor Speed: 2.66 GHz
Number Of Processors: 1
Total Number Of Cores: 2
L2 Cache: 6 MB
Memory: 4 GB
Bus Speed: 1.07 GHz

Mbox 2 Pro:

Manufacturer: DIGIDESIGN
Model: 0xA9
GUID: 0xA07E0100A90000
Maximum Speed: Up to 400 Mb/sec
Connection Speed: Up to 400 Mb/sec
Sub-units:
Mbox 2 Pro Unit:
Unit Software Version: 0x14001
Unit Spec ID: 0xA02D

I doubt any of that helps but I'm really not sure what to look for. Honestly, Pro Tools has been nothing but problems for me. The installation and registration was extremely tedious and time consuming, all sorts of seemingly unsolvable errors keep coming up and digidesign is no help. I have nothing but this site. please help

[dero]

In setup>playback engine set RTAS processors to 1 processor

Remove/disable[ctrl+command click] all plug ins on track and check audio

move audio on to a track that is playing and see if the same error occurs

delete all prefs and wavecache for the session

(there is a utility on digidesign.com that can do this automatically)

Upgrade to the latest CS update

Hope one of these helps