Using QNAP TS-453U-RP Version 4.3.3.0188 with two NICs setup (two different LAN segment). Had not been able to add it to Veritas Backup Exec 16 as "File server or NDMP data server" to backup the shared folders in QNAP.
The issue was because the Sys Admin has hardened the QNAP security due to recent malwares attack (WannaCry) and other cyber security threats. He has limit the networks segments which can access the QNAP.
To resolved the issue, access to QNAP web interface --> CONTROL PANEL --> SECURITY --> SECURITY LEVEL. Added the network segment which requires to access the QNAP.