Mdx problems

i have imported couple of models to my map, than i take a unit and changed it's model to the imported one, as i placed it in the editor, it showed me a green-black box
and said it couldn't load, so i saved the map and reopend it, than it worked..
but than after i closed the map and every time i opend it again, it shows me black-green boxes again... why =[

You just screwed up the import somehow.

Delete the imported file and change the unit's model back to the default one. Save. Reimport the model and save again. Then set the unit's model to the imported model.