[away3d] How to dinamically change materials of BSPtree child-objects?

[Baraba]

I created BSPTree :

[Embed(source="BSPdatoteka.awd", mimeType="application/octet-stream")]
private var BSPFile:Class;
...
_tree = BSPTree(AWData.parse(new BSPFile(), {customPath:"./
images/"}));


I want to change material of specific object in BSPTree...
I tried something like this:

CentralMaterialLibrary.updateMaterial("stand_S_2", _probeMat);

 ...nothing happens. Please help.