Maybe you need to (require 'ox-md) in your init file? Peter Davis writes:
> I'm looking at http://orgmode.org/manual/Markdown-export.html, which > says I can export to markdown, but these options don't exist in my org > installation (8.2.10). If I type C-c C-e m, I get 'Invalid key' > > Do I have to install something else? > > Thanks! > -pd -- Professor John Kitchin Doherty Hall A207F Department of Chemical Engineering Carnegie Mellon University Pittsburgh, PA 15213 412-268-7803 @johnkitchin http://kitchingroup.cheme.cmu.edu