Sorry for the two posts in one day, but how do I open my server's nether file in MCedit (bukkit)

It says this world has not been generated when I tried worldname_nether. I still have DIM1 and DIM-1 from when it was a vanilla server (I think its vanilla that uses those) but still no luck in opening them. I had decided I would just preserve the chunks with the old fortress and blaze farm, and regenerate the rest but it seems like a more difficult process than I had planned. Is there a simple way to open my server's nether in MCedit? I can load the overworld just fine.