I finally found the problem, it was the permission problem.
I originally thought that when I create a db using

dbmopen(%DB, 'file', 0666)

it would create a database file with the permission specified (0666) if the file doesn't exist
and also I thought the db file would be "file.db" The real db file somehow (on the RedHat)
has no extension and the permission was set to (0644 when investigating with the ls command)
I still have no explanation to myself why though!
but the problem is solved, thanks :)

-perlkid