Slenderman Monster

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No, you didn't do anything wrong, except for the fact that you forgot to skin your mesh to the joint. (which shouldn't be the cause of your problem) Like I said your mesh file is probably broken in some way and you should export a testfile with nothing but a simple cube skinned a single joint to determine if that is the case.
Just out of curiosity, how many triangles does your mesh have? Its the Number you can see under "Tris" in Maya in the top left corner of the screen. (If there are no numbers visible in your viewport, activate Display>Heads up display> poly count.)