When a native C4D material contains a layer shader, this layer shader is rendered black, no matter what it contains.
This is probably also the reason why a converted C4D material that contains a layer shader will end up as a Corona material with an empty layer shader.
Also take a look at "Mat" (the leaves material). Although everything looks fine (in the preview and also in the black and white texture representation of the texture in the alpha channel), obviously the wrong layer set is used. Just open the "choose layer set" setting to check.