Suggestion:
Start from scratch and verify that the installation and configuration was done correctly.
(You never mentioned the NBU, SAP or O/S version)
NBU 7: SAP Administrator Guide for UNIX,Linux
http://entsupport.symantec.com/docs/340133
NBU 6.5: SAP System Administrator's Guide for UNIX and Linux
http://seer.entsupport.symantec.com/docs/290217.htm
Start by verifying agent was installed correctly (no separate installation for NBU 7, see 6.5 manual for details).
Verify symbolic link was done correctly:
( ln -s /usr/openv/netbackup/bin/backint /usr/sap/
SID/SYS/exe/run/backint)
Verify your backup script - compare with sample scripts in the manual.
Verify your init
SID.utl and init
SID.sap configuration files - see required and suggested parameters in manual.