Huh? Are you asking us about how to import model portrait files?

. Otherwise if you are using the RoC World Editor then it will not work. In other terms if you have the TFT World Editor, then there is no Art - Model File - Portrait because portraits are only meant for the model meaning the portrait is already attached to the model but must be imported though.
Plus, however if you are talking about portraits then ... only doodads should have an Art - Model Portrait. There is no other updates that make this happen. Although if you haven't gotten updates from signing up to Bnet then you should.
If you weren't talking about portrait files then you mustve imported a texture wrong or you never imported texture correctly or one texture is missing ^^.
*Off Topic* You should introduce yourself and make a thread on the Introduce Yourself Forum, War Spirit! Cuz we would like to know what you can do in Warcraft, well am not forcing you to do it if you don't want to though. But anyways ... welcome to the Hive man!