DDS_Support,
The Y: that you see in your backup selections is the mapped network drive. You need to uncheck that from your backup selections and add the UNC path to that same network share.
Follow instructions on this technote to create a User Defined selection for the UNC path you would like to be backed up - http://www.symantec.com/docs/TECH23840
Also see this technote http://www.symantec.com/docs/TECH14963 - Network Attached Storage (NAS) appliance compatibility with Backup Exec 9.x, 10.x, 11.x, 12.x and 2010 R1/R2/R3 (NON NDMP)