A failure to launch issue has been reported with Pro Tools 11 after simultaneously running Final Cut Pro X and Pro Tools 11 with the Video Engine enabled. The first time this circumstance is met Pro Tools and Final Cut Pro X will operate together normally.   However, the next time Pro Tools is launched the application will hang at Initializing Audio Engine.  This launch failure will persist until Pro Tools is deleted and a Pro Tools bootcache file is removed from the system.

Locating the Pro Tools bootcache file:

In Finder, Click the Go Menu (or Shift+Cmd+G)
Type in "/private" (without quotes) and press enter
Open the var folder
Open the db folder
Open the BootCaches folder
There will be several folders in this directory that need to be explored in search of a file called "app.com.avid.ProTools.playlist"
The name of the folder that contains "app.com.avid.ProTools.playlist" will vary on each system.
Once you have located "app.com.avid.ProTools.playlist" drag it to the trash and empty the trash

After you have deleted "app.com.avid.ProTools.playlist" reinstall Pro Tools 11