Mapped Drive Back Ups

I have a windows SBS 2008 Server as my Backup Server. I have installed the Urbackup Client onto a PC that is an internet only client. It will back up a directory (C:\Users\Documents). However it fails to connect to a mapped drive directory (P:\Quickbooks) for back ups. I get a consistent error of: Connecting to ClientService of “Joel-PC” failed - CONNECT error during filelist construction. I am unsure of how to back up a mapped drive. Any advice?

What is the drive mapped from?

A NAS device that is on the network.

Do you know the model? Some NAS would allow you to install the backup software on them natively.

DS212j Synology Diskstation