"This code is already assigned" When Altering codes.

I was trying to change my code for the door lock (Kwikset 910) from the Alarm.com site and I get an error stating that “this code has already been assigned”. There are two other door users and both of their codes are different.

Why could this be?

When adding user codes through Alarm.com, you will also be unable to use any locally added special codes such as the installer code or duress code.

Were you attempting to possibly use one of these?