cannot read property 'elements' of null

Chrome is showing error "cannot read property 'elements' of null"

here is the code

function DisplayFormValues(){
        var str = 'proType=4&send=y';
        var elem = document.getElementById('form2').elements; // error on this line
        for(var i = 0; i < elem.length; i++){
			str += '&' +  elem[i].name + '=' + elem[i].value;
        } 
		//document.write(str);
		return str
    }

Code (markup):

What's this? How to fix? Please help

 

try
document.forms['form2'].elements

 

Thanks. It worked. +Rep for you.