Why does my user-created Unicorn crash Zoo Tycoon 2

It was a Common Zebra linking to the Forest/ Grass and Branches Unicorn Zoopedia till I coded the .bfm's. Now the icon shows up (with a green box around it), but if I try to place it, it's invisible and the game crashes! Why??? (Note: I use GMax for meshing, and I have the .nif plugin, but I can only export .nifs. Try to import them and they will be invisible. (?) Please help! I have to finish my UXP!