Try to follow these steps:
(*) Create a plane (ground) and one sphere.
(*) Create CScatter and try to scatter 200 sphere on the plane.
(*) Use a Cellular as a density map for CScatter.
(*) Drag&Drop as ISTANCE the Cellular in an empty slot in the MEdit
(*) Ok, we don't like Cellular and I prefer, for example, Splat. Click the "Cellular" button on the MEdit (right side of MEdit)
(*) Select Splat (Discard old map)
(*) 3ds max freeze.