If a keypad is not communicating for some reason at the time a tenant is vacated that keypad may not get the delete command from the computer. In this case, once keypad communication is restored, you will need to Zap Codes and re-upload. Please note that you should ONLY do this if you are SURE the keypad is communicating. I.e. you can see recent activity for that keypad in your activity window.
Open Guardian Control Panel and right click on each keypad that still has the old code stored. Go to commands -> Zap Codes
Zapping codes clears ALL codes from the keypad so you will want to re-upload them right away. To do this go to your management software and upload all codes. In QuikStor Express this can be done by going to Tools -> Upload All Key Codes
The codes can take 10 – 15 minutes to load into the keypad depending how many units you have. Give the keypad at least 15 minutes to update and then go try the code again. It should no longer work.