You don't have root on CM and so you can't wireshark from it's server on your own.
Many alternatives are available. Get your LAN guy to port mirror the CM to another network port and sniff it with a laptop.
You could tell the Ericsson guy that you spoke to somebody on the Internet and you know what's up and he should quit complaining and send you a wireshark trace
Or, if you're on system platform, from dom0, you can "tshark -i avpublic host 1.1.1.1" presuming the far end signaling IP is 1.1.1.1 and that'll print packets to your terminal. if you add a -w /home/cust/myericssonpbxisbroken.pcap then you can take the packet capture off later with winscp or something.
You shouldn't be running wireshark on live PBXs and if you forget it and leave it running, you might really screw things up. Nothing wrong with getting the LAN guy to mirror a port besides it being a little slower to get done.
But even before you wireshark, you can display alarms and errors on that signaling group, you can test it in CM and get all sorts of error and failure codes that can tell you what's going on without resorting to looking at raw packets - like if they're actually talking or not, you'll get something to clue you in on that. Your Ericsson guy won't care, but at least that way you can feel like a tough guy when you send him that wireshark trace later.