Can you tell us, if your server is fully updated (no updates are offered any more if you click the
Update now button in the console on Settings/General) and which version numbers are shown in the console under Settings/Ressources?
If the system is up to date, uninstall the connector software from the client, open the website
http://server:55000 (replace server with your machines name) and install it from here. Or run setup.exe in the Home Server Connector Software folder in the Software share on your server.
If this also not works, what is the exact error happening? Which security suite is running on the clients?
Best greetings from Germany
Olaf