I am guessing that the "Player 2/3 from Players on Team 1" is returning -1, an invalid player. As such you are trying to create units for player -1, which is illegal.
Basically, there is no player 2 or 3 in "Players on Team 1" player group.
You can confirm using the trigger debugger, and stepping through the initialization function while watching what values are assigned to what variables. In fact, I am quite surprised you did not use this already.