Are you clicking yes to XFROG compatability? Try loading the original dl'd trees using the tgo reader, you might have better luck. The freebies have given me no problems at all, and a cactus I had left over from an assignment/commission piece that was originally XFROG and exported for me to use as an .obj and came with all the .tif files as well as the .mtl for the obj worked well. If you are using an .obj with a .mtl file the maps still need to be in the same dir or it won't work I've found as I forgot to move them there at first and got a blank cactus. If my pic ever finishes rendering I will post it here as an example.