We have a small intercom (Viking) in our front lobby that rings through a CO line to an ACD group, that has been working for years. A couple of weeks ago out of the blue it stopped working.

I've physically replaced the unit, you hear the box generating a ring tone, but it never rings to the folks logged in to the proper ACD group.

I've poked around on the System Programming screen, changed a couple of things but when they didn't correct the problem all settings were reverted to what they were when I started troubleshooting.

A little bit at a loss now as to where to take this troubleshooting. Any ideas?