post-boot is not executed - what's wrong?

[sbn]

Hi i have a 500gx with oleg' WL500gx-1.9.2.7-5a firmware

my post-boot file contains

p910nd -f /dev/usb/lp1 1
echo bla bla bla > testfile

and it's located in /usr/local/sbin, and i've given it a chmod 777

when i run the post-boot manually, it works fine, the testfile is created and i can see the p9101d on the list when i type ps

but when i reboot the device, the specified p910nd is not loaded and the testfile is not created.

what did i do wrong? of course, the flashfs is enabled and so...

EDIT:
nevermind, i forgot to insert the

#!/bin/sh

in the beginning of the file