Why is there a red X on Seats on the schedule

I set up a schedule , configured the seats.  When I try to activate the schedule. The schedule stays red and the seats red X is on.  The X doesn't say anything when you put the mouse on it.  I reconfigured the seats again. And it says its good.  Activate the schedule. And red X lights up

Did you remember to assign the seating configuration to the airplane, at the Fleet Manager Page? Tick the box next to the airplane, and then in the bottom assign the seating configuation.