Firebug says I have undefined variables. I'm not sure why.

My if doesn't add the disable.

Code JavaScript:
addOnload(function(){
	var country = document.accountsettings.country.selectedIndex;
	var country_text = document.accountsettings.country.options[country].text;
 
	if(country_text != 'United States')
		{
			document.getElementById('state').disabled=true;
		}
	else 
		{
			document.getElementById('state').disabled=false
		}
});