Test your newly created Shell Script
#sudo bash /home/rmalla/backup.sh
--- NOTE ---
I spent about an hour trying to figure out why my script did not work, and the answer was that I had created the script in Notepad and uploaded it to de web and it had some hidden flags that did not allow this to work.
To check if you have this problema run
sudo cat -A /home/USER/backup.sh
#USER:~$ sudo cat -A /home/USER/backup.sh
#tar cvzf $FILE OpenbravoERP-3.0^M$
The ^M is whats causing the problem.