Auto Lock "not operating properly" warning sound

[Tornado2 1]

My auto lock is now almost continually failing. When this happens it gives a loud double beep (instead of the normal low beep that it's going to lock) and then doesn't lock.
Anyone else have this happen? It started as once in a while and now almost always.
I've open/close the door and get the failed double beep again.

This is the only reference I could find in the manual. No real reason given:

If the auto lock function does not operate properly after it is activated, the auto lock operation stop beeper will sound.
If the warning beeper sounds, check that you are carrying the keyless remote. Then, open/close a door and confirm the auto lock activation beeper sounds once.

 

[Trail_Jogger3]

Does it happen with both remotes? If just one is a problem try replacing the battery. The double beep means the car doesn't sense the remote outside the car so it doesn't lock. (This occasionally happens to me if I close the liftgate and walk away too quickly before it locks.)