If the motor was started with the throttle even slightly open, the engine computer, EMM, senses that something is not right and will not allow the motor to accelerate. If the throttle linkage, throttle shafts, or postition sensor on the motor are a bit sticky or corroded, one or more of the items could keep from returning to fully closed.
The same thing happens if the shift switch on the motor is loose, out of adjustment, sticking, or faulty. In that case the EMM thinks that the motor is still in neutral and will not allow it to rev up.
If it does not operate correctly when you are sure the throttle is completely closed on starting, see your Evinrude dealer for assistance.