[away3d] Help! RangeError: Error #1125: The index 0 is out of range 0.

[eco_bach]

get the following bug

All I am doing is grouping 4 cubes (addChild to a ObjectContainer3D
object) and then taking the resulting ObjectContainer3D and adding to
stage

RangeError: Error #1125: The index 0 is out of range 0.
        at away3dlite.containers::Scene3D/removeSceneMaterial()
        at away3dlite.core.base::Mesh/buildMaterials()
        at away3dlite.core.base::Mesh/updateScene()
        at away3dlite.containers::ObjectContainer3D/addChild()

Can anyone suggest what my problem is?