Okay let me run off a few questions to see if this has already been done and then let's see what we can do to help..
When you started building your map you started it as new arena....and got the red map while you was making your map
Then when you was in your build section you went to the arena tab and set numbers of players to 2 or above....8 is exceptable...
This I believe we accomplished that you already did... Now when you start your game what does it say? or do?
Also if you can send a screen of the game in startup if it is going to single player....
Have you downloaded your CLiPs today.