Backup Server may issue an “Access denied” message when you try to dump to a device mounted from across a network.
By default, all Windows services are started by using the “LocalSystem” user account, which does not allow the service to access network-mounted drives, for example, NFS, NetWare, or NTFS mounts from other machines.
To work around this restriction, configure Backup Server to start with a regular user account, rather than the Windows default account. The user should have the permission to access remote drives.