I am brand new to express scribe and having troubles of my own with hot keys BUT I had the EXACT same problem with the first tape I tried to load. In the end, it was NOT a problem with express scribe but something to do with the way it had been loaded by the sender. Try having someone else with a Mac try to open it and see if it might not be your system.
Hope this helps at least a little - I know the frustration!
tillie2