1. Did you make sure to delete the war3 line?
2. Did you restart world editor after importing a model?
3. If you did respect #2 did you open up the map that you imported the model into?
4. Are you sure the model you downloaded is working? Ask someone else that downloaded it if it works or look at the moderator comment.
5. Are you SURE you did everything right?
If you did everything then I really have no idea.