Try the following steps in order - one by one. If one doesn't help, proceed to the next step.

1. Pro Tools LE version 5.2 is not compatible with OS X. If your mac is running OSX, reboot off of OS 9.x and reinstall Pro Tools LE.
a: Choose System Preferences from the Apple menu
b: Choose Startup Disk from the View menu. The Startup Disk pane appears, and the current startup System Folder is highlighted.
c Look at the lock button
If the lock button appears closed, click the lock to make changes. Enter an Admin user name and password, then click OK.
d: Click the System Folder icon of Mac OS 9 volume you wish to start up from. When many choice are available, move the slider bar to see additional choices. A gold "9" badge appears on the icon of a Mac OS 9 System Folder if it is located on the same volume as Mac OS X.
e: For Mac OS X 10.1 and later, click the Restart button. A confirmation dialog appears (Figure 5). Click Save and Restart. Note: In versions of Mac OS X prior to 10.1, the restart button does not appear here. Instead, choose Restart from the Apple menu.


2. When the Sound Control Panel is set to Digidesign (instead of Built-In) other programs are able to use the Mbox for audio playback. Digidesign hardware is designed to allow only one program to use it at a time, therefore a conflict can occur if Pro Tools LE is launched while another application is using the Mbox (even the Mac OS can take control of the hardware).
- Setting the Sound Control Panel to Built-In and restarting the computer should resolve this error.
- If "Digidesign" is chosen as the output selection for another application, such as the software synth "Reason", Pro Tools LE won't launch and gives the -6009 error. You make any application that had been using Mbox hardware releases it's hold by choosing something other than "Digidesign" as it/s output selection.
Example: Launch "Reason" and change the output of the synth from the "Digidesign" choice to something else.

3. Trim extensions as specified by Digidesign:
a: From the APPLE menu, choose Control Panels > Extensions Manager
b: Choose "Mac OS9.x BASE" as the selected set.
c: Click "Duplicate Set" at the bottom/right of Extensions Manager
d: Give the duplicate set a name, like "ProTools" or "Music" and click "OK".
e: Scroll through the list and turn ON (place an X in the box next to) the following items:
- Digidesign (any control panel or extensions that starts with Digidesign)
- Digisystem INIT
- Open Music System
- USB OMSMIdi Driver
- any other 3rd party driver needed, like "MOTU USB Driver", MidiSportDriver" etc
f: click RESTART at the bottom of the window. The new extension set will then be active.