We went from CM 4.x to CM 6.1.2. We have several people that use IP Communicator. If they are on the LAN, works fine. If they are connected via a site-to-site VPN, works fine. If they connect through an SSL VPN and then Network Connect (it is a Juniper SA 4000 SSL VPN), it is unpredictable. Sometime, we start it and it sits there for 15-20 minutes, and then it finally works. Sometimes, it doesn't ever work. Very rarely, it works right away. People had no problem with IP Communicator through the SSL VPN when we were using CM 4.x.
We did have IPC set up to use SCCP, but we changed it to SIP, and that seems to work, although we are doing more testing.
The new servers are on the same VLAN as the old systems were, so I don't think it is a firewall or routing issue. Does anyone out there have any ideas? I opened a TAC case, but so far we have had no luck in fixing it.