Linked object Groups not rendering

I have some nuts in groups linked to a file. They are all toggled to render, but not rendering ( image at right) although they show up on the render view (image left).

I would appreciate any help you can give.


Please supply a link to a demo blend file that shows the same results for review

Richard,
i do not understand why, while preparing a demo file I moved the groups to a different layer and they rendered!
thanks.

Maybe they were on a layer that wasn’t set to be rendered