Avid posted to their Knowledge Base site that Pro Tools 9 and earlier versions are not compatible with OS X Lion.
August 19th Update: Pro Tools 9.0.5 Update, Mac OS X 10.7 Support
Apple has released OS X Lion (Mac OS X 10.7). As of this writing Pro Tools 9 and all earlier versions of Pro Tools software are not compatible with OS X Lion. We are currently working with Apple in order to establish full compatibility with Pro Tools 9 and will notify you as soon as this work has completed.
The following devices and add-ons are qualified for use on Mac OS X 10.7 (Lion). Please visit www.m-audio/com/drivers to download the latest updates. It is only necessary to install the latest version; DO NOT install previous versions. For users that have upgraded from 10.6, please run the included uninstaller to remove previous M-Audio driver versions before installing the latest version.
Fast Track Pro
Fast Track Ultra
Fast Track Ultra 8R
Fast Track USB
ProKeys Sono 61
ProKeys Sono 88
* Note that Torq 2.0 is not qualified for use on 10.7 at this time