You have a custom material that you are trying to load from the Material Library but NX is giving the error "The specified material is not valid for assigning to the specified object".
You most likely already have a material assigned to the body and it will be listed under Local Materials.
If you want to use the Material from the Library Materials, you will first have to remove the material from Local Materials list. To remove the material from the Local Materials, go to Tools -> Materials > Manage Materials -> Local Materials -> select the material to be removed and either use MB3 -> Delete or select the delete Icon in the lower right.
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