node = tree.NodeByInternalName("PoserSurface")

It's better to use:

node = tree.Node(0)

The reason is because the internal name of the PoserSurface node isn't always 'PoserSurface'!

By way of example, check out BB's EnvDome - it uses the internal name 'Surface' instead, which wouldn't be picked up by your script.

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