Comcast Norton Internet Security Backup - Network drive not showing.

When I go to my Comcast Norton Internet Security Backup Solutions, under the "Where" option, I can see my "C" drive , my DVD drives, but not my WD Network Drive. Is this a limitation of the Comcast NIS program, that it will not let you choose a network drive, just a "USB" plug-in? My network drive is visible to this and my other computer and I transfer files there regularly in fact even "Quicken" will let me backup to the network drive. I don't see any options in the NIS Backup to allow searching for or connecting to a net work drive. Unless this is a marketing ploy to make you purchase another product. Why have an all in one security program, with severe limitations?

Thank you for your response.