I have a site that under mmc 406 the groups are changing for night and day for all lines.
They are using 501 for day and 505 for night. It changes back to 500 and 501.
They claim to have no power outages that would cause the pbx to be down

Well since default is 500 for day and night are you sure someones not changing the settings?Try changing the passcode and see if someone complains they can't program the system.
The memory is on the cabinet itself so it may be at fault.

We moved them recently and the same thing happened.

Chaz, What version is the DCS ? How often does this problem happen ? Have you tried changing the passcode ?

TCB

I will check next time I go. Every time I go there it has changed back.