ok using Spooner's suggestion I got the demo to work (removing map_misc from the mission.sqm addons list)
some thoughts from someone who believes in "idiot-proofing" everything. Napoleon used to keep a village idiot outside his tent while he wrote campaign orders for his Field Marshals. After writing the orders, he'd have the village idiot read them. If the idiot couldn't understand them clearly, he re-wrote the orders. Anyway, the point is, a good demo allows the casual downloader to load up the mission, be told what should happen and what to do right away
within the mission, not just in the readme. Anyway it wasn't totally clear what was going on at first and in fact my first few artillery salvos landed in the water and i thought the script didn't work. So you get my point, would be good to spiff up the markers, map, etc etc. for idiot beginners like myself