@ Keppel : the reason giving you the advice grouping before rigging is because you mentioned the 'no polygons found' pop-up
as well to make sure the names are absolute exact the same .. both groups & bones have to be simulair

Sorry for the confusion from my side .. unfortunate have to admit my technical skills not reach THAT far yet :/
But pretty sure there are around able to help you with this

Maybe posting a screenshot helps you to make clear what you mean exactly?

@ Rokket : thanx for sharing your knowledge! .. it helps :)