It means licensing has broken. There are two ways to remedy this:
Reinstall from your discs.
Run the License Repair tool. There is a .py script that you will be running in Terminal to do this if your OS is 10.7 or above.
Let me know how you fare.
Note: Restoring Photoshop from a Time Machine backup is a common cause of of this error. Always reinstall, never recover Photoshop from a backup.
Thanks for the instructions. I got it back and everything is running fine now! I used the license repair tool.
Ok. Mark the answer as correct then so others know it's been resolved.
The answer is correct!