Blender Object as Detail Mesh don't show?

Hi every one, I start to made an scenery using a terrain, and I want to add some detail mesh to it using some blender 3d models (rocks, stones, etc.), my question is:

Why can’t I paint with those objects?.

I search in the web but not good answer at all, this could be a version problem or what could it be?, any help will be appreciated, thanks in advance.

Note: I’m using Unity 3.4.2 and Blender 2.56b.

Hi again, I found that the problem it’s the hierarchy object generated when the blender object it’s imported, so, we only need the main object example: MyBloque(Blender File)–>CubeMesh(Object Inside).

We only need the - CubeMesh - and with that make a prefab to use like a Mesh Detail Object into the terrain.