Came across this error recently which is thankfully an easy fix but there is not a lot out there, the following is the error and the fix.
This Veeam server happened to have not been managed for a little while so this was not picked up, the backup repository would throw up the error when running a rescan.
Failed to rescan repository NAME error. Backup Console Version ‘126.96.36.1990’ is not compatible with install service on host
There would also be an error under Manager Servers
The easy fix is to patch Veeam to the latest available patch, once installed the error is cleared and the repository is working