You are seeing something like the following error message in the Message Logs of the backup:
"bnet.c:1011 Could not connect to Storage daemon on CFA-IP:9103. ERR=Connection refused
- Our services are not running on the client
- A firewall may be blocking the connection from the client to the CFA on port 9103.
- A quick backup of a reduced fileset (with "No Change on Full" enabled), should help diagnose whether the problem still exists after firewall changes or other network fixes