You prolly moved the sims skeleton in Milkshape.
Import your original base (maxis?) mesh first, delete the mesh groups and morphs.
Then import this mesh and export it again.
This way you give your mesh a new original skeleton.
Cant tell by the info your providing, but sometimes this also happens when mixing up Elder/Adult and teen skeletons.(like when your scaling a adult mesh to teen size but forget to give it a teen skeleton also.)
