what is the faile reason? the model's or my codes'?

my code in js script :

///

www = new WWW("http://192.XXX.XXX.XXX/UnityTest3/WebPlayer/AssetBundle/model1.fbx") yield www; var instance = Instantiate(www.assetBundle.Load("model1"));

///

In this way i load the "model1" in my scene. In the same way , when i load another model such as "model2.fbx",it does not work.

warnning in the console:

Failed to load asset bundle UnityEngine.WWW:get_assetBundle() $:MoveNext() (at Assets/script/RuntimeScript.js:38)

i don't know why.Both of them were exported from 3DMax to FBX in the same way. And one can be loaded,the other one can't be. Is the problem of the model's or other reason? :(

i need someone's help.thank u very much!