Attempting to backup a Windows Server 2012 R2 Server with the Veeam Agent freshly installed and Backup and Replication server version 9.5 (also 10). The administrator credentials for the source server had been added to the destination server (Backup and Replication) and a backup job with type Windows Agent Backup was created. When running the job it would fail with error: Processing ServerName Error: Failed to connect to x.x.x.x:11731
The reason is because the source Windows Server was not properly added to the infrastructure of the destination Backup and Replication server. Checking the Programs and Features installed on the source Windows Server, only Veeam Agent for Microsoft Windows was listed. The Veeam Installer service was missing, which is triggered to install by the destination Backup and Replication server.
To resolve it, from Backup and Replication server navigate to Physical Infrastructure, Manually Added. Then perform a Rescan. Once complete you should see a confirmation that the Backup agent is installed on the source Server. Checking Programs and Features of the source Windows Server 2012 R2, the Veeam Installer Service should now be listed as installed. The backup job on the destination server can now be restarted and should complete without the previous failed to connect error.