This might work
Not sure if this will work, load the MP project in JK radient so that it shows a blank map, now click "Edit" (I think it's Edit! I'm at work so I'm not sure!) then click "load prefab", select your map, it should then hopefully load your map into the MP project - compile and then test in MP......
Hope this works, I'm not sure, but it's worth a try
"In the dark, see past our eyes"