System Definity G3SI...The send call button was flickering on users phone when pressed and not activating. Phone was an old 8410D, swapped phone with a 6408D+. The same result, it would not take by pressing the designated button on phone or by the FAC code. Tried a busy and release of the station, still the SAC would not take?? System is programmed in Abrv. dial list on phone... Any ideas on what to check?