i had a similar problem with one of my maps, i removed all starting locations and set the map to one player, saved and reopend it, put it back the starting locations changed the number of players back and finaly saved it

that worked for my map, maybe not all steps are necessary...

tried it... didn't work

I set the slots to player and saved it then load it and set the slots to empty and it worked
now theres just a gray box in the middle but it can't be selected

it worked thanks for the help

I was just playing S'klar's map. at first when i was trying to load the map it went to 95-99 and stopped. so we kept trying to fix it when S'klar did something and it let me play. so we went it. then, once ''we'' got in it said ''out of snyc'' and S'klar was in the map but i wasn't. instead i was in a blank area with all of the AI's in the middle with me. it was very... very odd.   

P.S.
we were domin against feddys
and this was on his 6 player map.