Syed,
Backup Exec ver 10.0 has been designed to automaticaly exclude any database files, and because of this even though you select the files to be backed up, they are skipped and it will not report any errors. There are 2 ways around this which were explained by the Veritas guy:
1- You can buy the Lotus Domino agent or
2- You can follow the support document listed in his comments. Which basicaly tells you how to go into the registry and disable the automatic exclude option.
I personally recommend following option 2 first because it wont cost you anything to start with. Run a full backup and test restoring some NSF files to make sure everything looks good and that you're not getting any errors. If it works great. If not the only other option is 2.
Good luck :)