Do you mean creating a Duplicate copy of you exisiting backup ? or to you want to backup data to the network drive ?
You can create Backup to disk folder on the network drive and perform backups as well as duplicate backup set to the backup to disk device.
Mapped drives to a server do not work and are not supported.
If it was iSCSI, then it would work...a normal mapped share to Windows doesn't.
Make sure that you are using an account with admin rights to that share.
If it is a NAS, try enaling iSCSI if available and then carve out iSCSI LUNs before presenting them to your backup server.
Make sure the account which you are using has the rights mentioned in the below
If you have recently changed password for the BE account than update
credentials through BEutility.exe
OK...something else you can try:
1. Do a repair of the BEDB. USe the TN below:
2. Repair Backup Exec using Add/Remove Programs.
3. If you have an antivirus on the server, make sure that it isn't perhaps blocking BE from working properly.