This could be an issue with the Current Engine setting in the Pro Tools Playback Engine.
Mac and Windows
This has been resolved in some scenarios by picking a different Playback Engine:
This should allow Pro Tools to launch.
If the solution above fails, you can try deleting the “com.apple.audio.AggregateDevices.plist” preference on Mac OS X. You can find this preference file in the following location:
Driver Updates (Mac and Windows)
If you are upgrading to Pro Tools (v9 or higher), please download and install the latest drivers for your hardware from the following page: