Nut upsuser - Jul 2005 - Mustek 400va + NUT 2.0.1 shutdown problem

I've installed everything from sources (NUT 2.0.1) 
on freebsd 5.4 and it detects the ups, it tells me 
about the voltages etc.
When the battery charge reaches certain level it 
tells me that the battery is low and the system 
will shutdown but nothing happenes.
In logs I can only find:

upsmon[386]: Executing automatic power-fail 
shutdown
upsmon[384]: Unable to call shutdown command 
/sbin/shutdown

I don't have a clue what could be wrong....
Anyone could help me ??

Cheers, Greg