So, I'm concerned with your problem (because I've never seen that before). Please check if you have these files:

$ locate powerbtn
/etc/acpi/powerbtn.sh
/etc/acpi/events/powerbtn

Into /etc/acpi/events/powerbtn make sure that you have at least these lines below:

event=button[ /]power
action=/etc/acpi/powerbtn.sh

(yes, it has a space between 1st bracket and slash)

Check also if the script powerbtn.sh is in its place.

Good luck