Help... How do I stop a script from running?

I have a script that runs once I tap a button ... the script listens for the users head to nod.

Everything is fine first pass through.  

When I'm done I am calling event.enabled = false to stop the script and that works. 

When I reset everything back to the main screen.. that initial button tap doesnt run the script.  I put a print statement so I'm sure the script gets called.

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This is the script. 

var nodSamples = [];

var runOnce = 0;

function update (eventData)

{

var headTransform = script.headBindingObject.getTransform();

var headForward = headTransform.up;

var headForwardNoY = new vec3( headTransform.up.x, 0.0, headTransform.up.z )

var dot = headForwardNoY.dot ( headForward );

if( nodSamples.length >= script.numNodSamples )

{

nodSamples.shift();

}

nodSamples.push( dot );

print("Checking for Nod")

checkForNod();

}

var event = script.createEvent("UpdateEvent");

event.bind( update );