To troubleshoot this problem, first need to make sure the server's file sharing is enabled in the network. for example, you should try to access //server from the client pc, if the client PC has permission to access the server(in lan), you should be able to see the shared folder
only when the client has access to one of the shared folder, then only the client can transfer the backup data from the server to client PC and the current login window user must have the read access right to this folder.
Please login to the server and right click "Share with", Please select the windows users and assign the right to this user.
go back to client pc and close QnE System and open again, try to backup.
Note: Please take note that, if you are still using the version before 2015.0.0.3, you can only backup from the server, please make sure your version is 2015.0.0.4 or after in order to perform the backup from the client.