1- green cube = missing texture, wrong texture path, model uses other than blp texture
2- crash on load = messed up global/sequences, geoset animations have missing geosets, messed up nodes and others.
3- texture is all white = most likely mip mapping error, non-standard texture dimensions and/or texture dimensions above 512x512 and game did not scale them down correctly.
4- model not showing(only shadow does) = no idea, corrupted blp/mdx probably.
if you downloaded it off the site and the model is approved yet still displays a green cube
it's 99.99% likely you imported textures in wrong paths and/or missed some or that you imported a model that uses a texture from the frozen throne/later patches but is not present in your version of the game.