After I posted this, I was double-checking my IP settings and noticed that the DNS server address on both Remoterig units was set to point to my WIFI range extender instead of my router. Now, why that would cause an intermittent SIP error, I don't know. And I'm not sure that it was THE cause, but so far, so good after resetting both to point to the router. I did check my router and SIP ALG is disabled, although since I'm totally inside the firewall with all this, I don't know why that would matter...ditto the SIP ports. Both Remoterig units have static IP addresses and point to each other. A simple setup. Let's see if resetting the DNS entry solves the issue. Thanks for your help!