PROBLEM:
There was no endpoint listening at http://xxxxxx.com:8021/DiagnosticService that could accept the message.
SOLUTION:
- Check the ports and make sure they are correct.
- Make sure there is not a conflict with the port number
In this case, try changing the port number from 8021 to 8001
Add TCP port inbound firewall rules for ports 8000-8012 to Central and site database hosts