As has been said the 'no go' to the summit from the train terminus at the Ptarmigan area has been operation since the system was built....but applies only to summer visitors.
In winter if you have skis, snowboard or even snowshoes you can go and get lost anywhere in the Northern Cairngorms having ascended on the train.
So summer visitors even on a windless sunny day are kept indoors. Erosion? there is a granite staircase with posts and handrails that I guess that most folks would use in summer.
I have only used the train in winter to gain access to the upper skiing area.
Totally closed yesterday, gates closed in Glenmore, after the wind had dumped metres of snow on the access road to the carpark.
It is the mid-term holiday period so I guess that it is real downer for skiers and for the providers of the ski service.