In the previous version the viewer could not show meshes with more than 65536 vertices. This limitation has now been removed.
The change appears in version 1.2.0 (Version number will appear on the main menu).
In the previous version the viewer would load the model, but only show the meshes that were smaller than the limit. It should now be possible to show much more complex meshes.
The limiting factor to model sizes may now be the amount of RAM required for the model.