NifViewer crashing on Rebone Unit

[Refar]

I am trying to rebone a unit, following Rabbit, Whites tutorial, however every time i am done and try to save the result the nif viewer crashes.

I tried different settings when exporting the unit, tried attaching the bones in different order and some other more or less promising ideas.

Now i am out of ideas... Has someone encountered this before ? Or maybe can suggest some possible cause/solution for this ?