Biped ragdoll problem

i just need some help ,

i already have exported character + BIPED skeleton from 3ds max to ue4 and until now all work fine , i follow some tutorials and i make the model to follow me and attack me , but the problem is when i set up the ragdoll to the model .
When i press simulate , the hands , legs and the head become simulate detached from the torso ( falling apart )

Thanks so much for the help !

i record video to show you , what happens.