[Kamailio-Users] Need Assistance Tracking Down A SIP Signaling Problem

Hello, I am wondering if anyone can help me determine what the problem with my SIP signaling is here. I have attached two Excel files (can provide other formats if someone doesn't have Excel). The environments in both scenarios are almost identical... although I am dealing with two different carriers upstream. In my environment, I have Kamailio (1.5) sitting in front of a multitude of Asterisk machines. I am using the dispatcher module to distribute INVITE requests across the network. I am doing some interop with a new carrier and we are struggling a bit with some looping scenarios. They are sending invites to my Kamailio server, I am forwarding to asterisk. The two XLS files (Success.xls) and (Fail.xls) have sip_trace information for the transactions. As you can see in the Fail.xls, the ACK to the 200 OK gets looped back to the Kamailio server and never ends up reaching the Asterisk machine. In the Success.xls, this doesn't happen. The only thing I can see that's different is the Success carrier appears to be replacing the RURI in the ACK with the value of the Contact header... in the failed one, the RURI of the ACK is the IP of my Kamailio gateway. I have read through the RFC 3261 to try and figure out what is breaking this, but haven't been able to. I basically need to determine if the signalling is correct... what is wrong with my config... and if the signalling is wrong, what the carrier is doing incorrectly. Thanks in advance! Geoff