As PJ said, make sure you have the proper quotas set.
Also, I've done two or three event builds that hit a schedule quota of 2,147,483,647.
It's just because the event build does too much at once.
Usually has to do with relays or hundreds of named brick.
I.e.:
onActivate -> NAMED BRICK -> setColor (Green)
onActivate -> NAMED BRICK -> setColorFX (Glow)
onActivate -> NAMED BRICK -> dissapear (3)
If you have, say, 150 of those NAMED BRICKs, then your schedule quota needs to be above 450 to operate.
3 events, 150 times, all at once = 450 schedules.
If you're using a complex relay system, there's some glitch that makes the schedules skyrocket.
It's happened to me before, and the only thing you can do is revise your system to use less.
It's best to check the quotas ARE set before re-doing your whole system incase thats the problem!