Problem with biped exporting

hello every one.
I have a 3d model in 3dsmax and it is rigged using biped . I had exported some animations successfully but after that I imported some non native 3d models to Max and after importing them when i returned to the model and tried to export some other animation to unity sth bad happend .
Here is a screen shot from my problem:

http://pic4up.ir/images/60026lso2xmm7c6amwca.jpg

As you see the hands are not natural!!!
but they are OK in 3dsmax!

Thanks for any help.

not sure if this is it but this happens sometimes when ‘segment scale compensate’ is on for any of the bones before you bind your skin.

I would try to first center all origins of both the armature and the mesh , second i would try to check the scale of the mesh compared to the armature , and last I guess u can check the parenting and the weights.