The only thing that I can think of is to make sure that the polarity is correct on all of the lines. Trunks on Mitel ports are polarity sensitive.
I checked the polarity and changed to check, but problem is still there. I even just to check changed the polarity on the working line and everything kept on working on that line, it still rings.
Sounds like a 50. Check each trunk in cmd 5xx reg 4. If polarity was the issue you would be getting alarms. What are the trunk equipment numbers? Can you direct trunk access them each?
This is my 5xx reg 4 - 40530010000. Not getting alarms. Not working one is a LS/GS Trunk Card (MPD) 9104-030-025 and working one is LS/GS Trunk Card 9104-030-100-SA. I can direct access each trunk. I changed the 3rd line and attached it to the 4th line on the 9104-030-025 trunk and it started to work. I even changed the cord from one trunk card (9104-030-025) to the other (9104-030-100-SA) and all lines work in and out going. To me it seems that the card might be defective.