sparkyballs is spot on with this
This is one of the changes in SABnzbd 1.2.0
"Python post/pre/notification-scripts now require execute (+x) permissions"
https://www.reddit.com/r/usenet/comments/5nrfek/sabnzbd_120_final_released/
SSH into to your unRAID machine, cd "change directory" to where your post processing script lives.
And enter: chmod +x nameofyourscript.py