JavaScript "null or not an object" error

Question

I'm running the following javacript below to place horizontal scrolling text on the banner of my website. it works in on server and not another. I get the following error:

Error: 'this.mqo' is null or not an object

JavaScript:

function start() {
    new mq('m1');
/* new mq('m2');
    */
    mqRotate(mqr); // must come last
}
window.onload = start;

// Continuous Text Marquee
// permission to use this Javascript on your web page is granted
// provided that all of the code below in this script (including these
// comments) is used without any alteration

function objWidth(obj) {
    if (obj.offsetWidth) return obj.offsetWidth;
    if (obj.clip) return obj.clip.width;
    return 0;
}
var mqr = [];

function mq(id) {
    this.mqo = document.getElementById(id);
    var wid = objWidth(this.mqo.getElementsByTagName('span')[0]) + 5;
    var fulwid = objWidth(this.mqo);
    var txt = this.mqo.getElementsByTagName('span')[0].innerHTML;
    this.mqo.innerHTML = '';
    var heit = this.mqo.style.height;
    this.mqo.onmouseout = function () {
        mqRotate(mqr);
    };
    this.mqo.onmouseover = function () {
        clearTimeout(mqr[0].TO);
    };
    this.mqo.ary = [];
    var maxw = Math.ceil(fulwid / wid) + 1;
    for (var i = 0; i < maxw; i++) {
        this.mqo.ary[i] = document.createElement('div');
        this.mqo.ary[i].innerHTML = txt;
        this.mqo.ary[i].style.position = 'absolute';
        this.mqo.ary[i].style.left = (wid * i) + 'px';
        this.mqo.ary[i].style.width = wid + 'px';
        this.mqo.ary[i].style.height = heit;
        this.mqo.appendChild(this.mqo.ary[i]);
    }
    mqr.push(this.mqo);
}
function mqRotate(mqr) {
    if (!mqr) return;
    for (var j = mqr.length - 1; j > -1; j--) {
        maxa = mqr[j].ary.length;
        for (var i = 0; i < maxa; i++) {
            var x = mqr[j].ary[i].style;
            x.left = (parseInt(x.left, 10) - 1) + 'px';
        }
        var y = mqr[j].ary[0].style;
        if (parseInt(y.left, 10) + parseInt(y.width, 10) < 0) {
            var z = mqr[j].ary.shift();
            z.style.left = (parseInt(z.style.left) + parseInt(z.style.width) * maxa) + 'px';
            mqr[j].ary.push(z);
        }
    }
    mqr[0].TO = setTimeout('mqRotate(mqr)', 10);
}

Answer 1

The reason is most likely that there is no element with the id "m1". Place this line first in the start function to diagnose this:

alert(document.getElementById('m1'));

If it shows "[Object]" (or similar), the element exists and it's some other problem, but if it shows "undefined" it means that there is no such element in the page.