Rwy in sight,
As per FlapsOne's previous post, the problem here was on the airstairs....which are part of the aircraft. It is most airline's policies when using MOBILE steps (i.e. ground handling equipment) that the door is not opened unless that ground equipment is in place, braked, and stabilisers deployed.
The Boeing 737 airstairs appear from a hatch underneath the passenger door, and deploy almost completely, including the handrails, before the passenger door needs to be fully opened. Only problem is, door needs to be opened for the top part of the handrail to be extended and attached to the door frame.
Reverse is true for closing up the aircraft.....top part of handrail disconnected from airstairs, leaving a gap at the top, before the door can be closed.