Veeam error "The RPC server is unavailable RPC function call failed" when trying to work with a backup client after updating Veeam server.

See

https://www.veeam.com/kb2065

I recommend testing & verifying with the syntax given in the Veeam article:

Test-NetConnection -ComputerName "<remote_machine>" -Port 6160

Locate and copy the installer for VeeamTransportService

from C:\Program Files\Veeam\Backup and Replication\Backup\Packages

and manually install that on the host being backed up.

But for the error message in question, the key step is to also get the new installer for

VeeamInstallerSvc from the same directory (noted above)

and on the backup endpoint with the error, manually uninstall the old version and install this newer one.

Also see

https://forums.veeam.com/veeam-backup-replication-f2/manual-upgrade-of-transport-service-t16739.html

Background header image for this post by Sebastian Herrmann on Unsplash