Page 7-8 of "Getting Started with the Mbox" book/PDF states :

5 In the Extensions Manager Control Panel, do
the following:
• Choose Mac OS 9.1 Base (or Mac OS 9.2 Base
or 9.2.2 Base) from the Selected Set pop-up
menu.
6 Click Restart to restart your computer.

We know this to be incorrect, as Mac OS9.x BASE extensions set is a locked set, and cannot be altered. That means that ProTools extensions cannot be turned on in this set - so ProTools won't work.

The steps for using Extensions Manager before installing ProTools, are.

- Choose "Mac OS9.x BASE" as the selected set.
- Click "Duplicate Set" at the bottom/right of Extensions Manager
- Give the duplicate set a name, like "ProTools" or "Music" and click "OK"
- Restart the computer.
- Proceed with the easy installation of ProTools LE.