Can't answer - INPHONEX

I have two SIP lines with INPHONEX. They are both getting into Asterisk in the same way.

The problem I have is that one of the lines work perfect but the other does not.

The one that is not working the problem is that the caller will call and even if I answer the phone (the phone rings) the caller thinks that nobody answers and still calling. In other words, even if I answer the call I can’t talk with the caller: asterisk doesn’t answer the call.

I debug the SIP messages and the only difference I found is that they are coming from different servers.

Any ideas, comments or suggestions are more than welcome!