Have simply 2 phones and 2 extensions. Both extensions are in a ring group (mode is prioritized). When pbx is called it answers. 1st phone rings allotted time (20 seconds) then 2nd phone rings. 2nd phone rings exactly 2 times; then message is heard "the number you have called xxx-xxx-xxxx is not available". This happens regardless of the destination chosen for the no answer situation. I have reversed the order of the phones and the same thing happens, so it is not a phone failure.