3D Imposter Sprite Depth Map?

Heya,

I use the Render To Texture BP tools to render 3D imposters for some foliage of mine. Thing is, I want to get a depth map to use with pixel depth offset, but whenever I try to render the textures the Pawn spits out an error when accessing the materials array of the Generator mesh (The array has 0 length). I set up a mask texture, material override and mask channel, still no avail.

Any idea what I might be doing wrong? Any other general tips for using this for foliage? Is there a practical example of what the dedicated depth render might be useful for?

Best regards,
Damir H.