Check 2 things.
1. alarm act – see if there is an active alarm that the GK is not available or something like that. If the alarm is there, then the tenor is not able to contact the gk. If it is the internal gk, reset the unit.
2. if you have setup the epad area to allow only specific IP addresses, make sure that you have added the tenor’s own IP address as well or no calls will work.