I have a customer that is having an issue with the SL100 we installed two weeks ago. Intermittently there are analog lines going busy and are unable to be released. The secretary, extension 101, is the only extension with line visibility. When she hits the line button she hears a busy tone but cannot release the line. They have to reboot the system to get the lines to clear.

When you installed the system, did you perform the Auto Side Tone Adjustment to calibrate the CO lines?

Have you isolated the trouble? It may be a outside plant problem
and not an internal problem. You didn't state you have attempted that.