Skirmish won't work

Everytime I try to play a skirmish it said that the team setup won’t work and won’t launch the game. I have assigned the AI their difficulty and selected characters for them to be. And I’m at a map that can have the same amount of players I have selected. Any ideas of what to do to get it to work?

I haven’t run into that message setting up a 3v3 with 5 AI ‘players’. Are you doing unbalanced teams like 3v2 or 4v2? Any players set to random for team instead of red or blue?