The aircraft was on final approach. The left radio altimeter was defect and the crew was aware of this. They had decided that the approach would be flown on the right autopilot, probably assuming this would isolate the aircraft from the faulty left radioaltimeter. The crew did not understand that the autothrottle system is always connected to the left radio altimeter, even when the right autoflight system is selected.

As such, the aircraft was tracking the ILS nicely, however the autothrottle had closed the throttles to idle ('RETARD FLARE'). The crew may have noticed this, however because the aircraft was vectored quite close to the runway, the aircraft initially had been above the glide slope and had to lose speed and altitude at the same time, requiring much less thrust. The closed throttles did probably not present an unusual state to the pilots. However, the aircraft continued to lose speed and finally stalled at about 500 ft and could not be recovered. 

There is a good animation of this situation (in Dutch) on youtube.
You can find the complete official report on the Dutch AIB website.