Troubleshooting:No setting found for this machine's BackendServerIP
Check that your backend's hostname hasn't changed recently. All the database settings are bound to hostnames, so if the hostname is different now to when you first set up MythTV, there's your answer. Either change the hostname back or re-run mythtv-setup on the backend machine to fix it.
Also changing the IP from the 127.0.0.1 loopback address in setup to the servers real private IP on the LAN i.e. 192.168.0.2 can also cure this problem (if using the backend on the same machine as the frontend).