Autotrol 255, code 2400?

[Mastiff]

This controller lost it's way temporarily and gave an "err3". I learned that the optical sensor can be confused by being in direct sunlight, and it eventually got re-oriented after I put the cover on. During the confusion, it kept displaying "2400" on the screen, and it still does now even though it appears to be functioning normally. Does anyone know what this means? When it was having trouble, it would display "err3" while the motor was turning, then the motor would stop and it would say "2400" even though it has not turned all the way to home. The manual says nothing about it.