I have been troubleshooting backup errors. My clients show grey in the connector software and indicate a server error during backup.
I had to connect a monitor to my WHS and look in the event viewer. It appears my WHS has been overheating and rebooting during overnight backups.
Since it's a headless server, WHS connector software needs better diagnostics to help users understand what is happening to their hardware. I assume that hardware vendors will include diagnostics in their solutions but most users will use the connector software.