Sometimes, when you shut down or restart workstations, or restart the workstation service (Novosoft Backup Network Workstation), the server may “remember” remote PCs and continue showing objects that are already obsolete. When this happens, some of the workstations that appear after you select “Backup Network” may be empty.
Generally, the situation where you will need to restart the service should never happen. However, this is a right way to make the server re-register the workstation whenever you need it.
See also: FAQ | Network Server Backup: