Intercom from 480i to 57i ringing

I try to intercom from a 480i to a 57i and the 57i rings. I have auto answer and barge in enabled. I tried to 2 different 57i and they both ring. If I do a intercom from a 57i to a 480i it works and if I do from 480i to 480i it works. So it must be something with the way the 480i sends an intercom invite to the 57i that causes it to ring. All phones have the latest firmware. Please help!!!