How to: Copy Rig from other Avatar

Hey Guys,

hope someone can help me, I am getting very desperate. Ive got a bunch of humanoid models which work perfectly with Mecanim. I need to lower their polycount so I used the software "PolyCruncher" to reduce the polygons. I also tried 3DS Max's ProOtimizer modifier but this one always destroys the skins and materials.

After the conversion through PolyCruncher Unity says, that there are not enugh bones remaining. I tried to copy the Avatar from the original file through the lowPoly files rig settings but the model doesnt move.

Is there anything to mention using the "Copy from other Avatar" method? Any Idea how to use PolyCruncher and still get a mecanim compatible model?

As I said I am very desperate at the moment. I need a ton of files beeing low poly and am running out of time. Thanks in advance!