(PS I'm working on Maya 8.5)
I'm trying to model half of a head and decided to duplicate it on the opposite side to make it whole. I went to Edit>Duplicate Special (options), set the X scale to -1 to have an opposite effect, Geometry as Instance and Group Under as Parent. Whenever I push the Apply or the Duplicate Special button, it never does anything. I also tried selecting all of the vertices but that also failed... Here's a desktop image if people have to know the absolute details.
Thank you very much for reading!