volvo penta sx shifter troubles, appreciate some help

[spindriftbrian]

1998 Volvo penta sx drive with 3.0...boats been sitting since last year..put in water and shifter works fine in drive & reverse but neutral throttle button when pushed will not allow throttling up in neutral...tried shifting forward and back to make contact to no avail... button does push in no obstruction...just cant throttle up in neutral...all cables look fine, otherwise works great on water...any suggestions before replacing shifter entirely?
appreciate response in advance..thx