The client is currently on V5.1.x. and a remote connection from a V6.x SP Console to the client is succussfully established.
The V5.1.x client is then manually or automatically updated to V6.x.
No Backup is peformed after this.
A remote connection from the SP Console is then attempted again and a error message; 'Unable to connect to the remote server', is displayed.
At the same time the Console user notice that the client is still showing as V5.1.x in the SP Console
The Console uses different protocols to connect to a V5 and a V6 client.
If a V5 client has been upgraded to V6 but has not backed up again after the upgrade, the Console assumes it is still V5 and therefore tries to connect using the V5 protocol which does not work.
As soon as a backup is done after the upgrade the correct version will be shown in the Console and the correct protocol used for the remote connection.
Run a manual backup after the upgrade or wait for the next automated backup to update the client version on the Storage Platform