I'm also having trouble with controls. I own a MacBook Pro, I've updated to ExpressScribe 4.25 (from 4.05), and it doesn't want to register my hot keys for Stepping forward or stepping back. Nothing seems to work but play and stop.
I've made sure to tell the Keyboard system preferences to allow me to use the keys -- F7 for step back and F9 for step forward, to correspond to the key markings -- but so far, no good. Any suggestions?