Welcome to LQ,
Are you giving the command as user or root? It may be that you need to stop this program as root. Try prefixing the poff command with sudo, so it would be sudo poff If that doesn't work find the PID no and kill it, type ps -ax in a terminal and look for the program you want to stop, when you find it type kill "pid number" You will have to kill each instance of that process.
EDIT: when I say pid number I mean the Process ID number that linux gives the program as it is started.
Last edited by mrrangerman; 10-11-2008 at 12:34 PM.
Reason: add info