S+ Spell Binder barcrest problem

[idylewild1]

Have a S+ Spell Binder Barcrest which works great except when the bonus game is at "12" and only the lower switch is active the button does not work until it is hit sometimes 10-15 times. It will eventually work. At all other times this swith works perfect --- first try. I have also ran the button test using the top box test button and the switch works every time without a problem as indicated by the top box display changing from zeros to ones. Any ideas would be appreciated. This is a fun game to play.