I have a Neax 2000 IVS 1800 series software level. On occasion My UCD group for VM (Rapartee) will hang up. Dial 2500 (Pilot) and it will not go to any of the extentions programmed for it. 2501,2502,...etc. Dial direct (ext) and they come back as fast busy. Only fix I have is to reboot system. I have looked at programming and everything looks good. I have checked (and repaired) grounding. Does anyone have any ideas on what may be causing this?