Cannot perform backup to network drive

Win 7, Norton 360 v21.6.0.32

I can Manage Backup Set and set destination as my network drive (Z:) but cannot perform a backup. The message says to ensure device connected although it knows it's available as it gave me the option to select it as a destination.

Network drive is connected to Netgear DGN2200 router using readySHARE.

Any advice gratefully received to resolve this.