It doesn't look look like the mission creator has exported the mission to a pbo.
Install the the contents of that to "My Documents\ArmA\Missions\Warfare_Extended_Public_v100.sara", then you should be able to load it up in the mission editor, when you've loaded it, choose the save button, and select "export to MP Missions".
Alternatively, if you've got something like winPBO or similar, you could just stick in a PBO called "Warfare_Extended_Public_v100.sara.pbo" and then lob that into the MPMissions directory.
This is all assuming the island is Sahrani. If the mission is based South Sahrani use "saralite" in place of "sara" in the directory/pbo name.
Hope this is helpful