from my testing app

[pascal] V[0] := V3(-150, -150, 1.0);
V[1] := V3( 150, -150, 1.0);
V[2] := V3( 150, 150, 1.0);
NewtonTreeCollisionAddFace(Collider, 3, @V, SizeOf(TVector3f), 1);

V[0] := V3( 150, 150, 1.0);
V[1] := V3(-150, 150, 1.0);
V[2] := V3(-150, -150, 1.0);
NewtonTreeCollisionAddFace(Collider, 3, @V, SizeOf(TVector3f), 1);[/pascal]

you must have at least 2 faces in a collision tree.

is the actor mesh a ragdoll? in the next big release of newton there will be a ragdoll animation system