your whole program shuts down??? you get an error message? The program terminates?? If your having problems with importing models and this happens regardless of which file you import then you have a problem. Get the latest patch to warcraft expansion if you dont have it. If that doesnt work try reinstalling warcraft. Ive had wierd situations like that happen in the editor myself. Usually was fixed with a new patch.
Are you importing a custom model? Also does the editor automatically shutdown or only after viewing the model. If the latter is true sometimes saving the map with the imported model then shutting down editor and restarting it allows the model to be properly shown although stability of the program is usually sacrificed.