We have an Avaya S8720 switch, I have 3 ISDN Pri's going to another Switch that has 50 extensions off of it....Basically, on incoming call's sometimes the call is connected. Then when either party try's to go SECURE, it will drop. If they stay unsecure, the calls stay connected...Drop the idea of other switch being a issue, Im finding other ISDN STE phones are doing the samething. Any Idea's ?