I've created a mix between a whale and a cow using the cow skeleton. I could not find any tutorials on how to create custom skins for creatures, so I've just used what I've learned from the custom armor tutorials plus a bit of improvisation.

Everything seems fine in blender, nifskope and the creation kit, except when trying to create a actor using my custom skin. When trying to see the model in the actor's preview window, the CK throws an error warning at me saying:

And nothing but the grey void appears in the preview window.

Does anyone know what this warning means? I know you can attach either a 'Parent Node' or an 'Extra Data' in NifSkope but I don't know which parent node or extra data to add and where to add it.