Advanced Controls - List Box - Selection won't map to output

Hi. I am trying to use an advanced list box to select a beam section from the first column in a matrix that I can then use to lookup related properties further on in my calc sheet. The problem I have is that the selection does not get parsed to the output variable. Any help with this would be appreciated, I can’t seem to find anything useful online, but I am clearly missing some detail.

Here is the list box code and MathCAD file attached.
 

// TODO: Add your initialization code here

function ListBoxEvent_Start(Inputs, Outputs) {
   // TODO: Add your code here
};

function ListBoxEvent_Exec(Inputs, Outputs) {

	// 1. Clear the list box contents FIRST to reset it
   	ListBox.ResetContent(); 

	var options = Inputs[0].Value;

	 // 2. Loop through and add the strings
	for(var i=0; i < options.length; i++) {
	ListBox.AddString(options[i]);
	}
	// 3. Set your output
    	Outputs[0].Value = options[ListBox.CurSel()];
	//Outputs[0].Value = ListBox.get_text(ListBox.CurSel());
};

function ListBoxEvent_Stop(Inputs, Outputs) {
    // TODO: Add your code here
};

function ListBox_SelChanged(Inputs, Outputs) {
    // TODO: Add your code here
};

function ListBox_DblClick(Inputs, Outputs) {
    // TODO: Add your code here
};