Intercom from Aastra 480i to 57i

I try to make an intercom call from the Aastra 480i to the 57i and it rings. I have autoanswer and barge in enabled. It should just auto answer. I have the new firmware. If I send an intercom from the 57i to the 480i it works and if I send an intercom from the 480i to another 480i it also works. Any ideas?

What are you dialing to send the intercom call?

BF