Tooltip not Working on Mouseover event when page event call in Gridview Control

function SetTooltip() {
    var sPrefix = 'Tooltip.';
    //Getting all the elements from body which are Anchor tag
    var docElemnts = document.getElementsByTagName('a');
    alert(docElemnts);
    for (var e = 0; e < docElemnts.length; e++) {
        with (docElemnts[e]) {
            //Check founded Anchor tag is belongs to Tooltip
            if (getAttribute('rel') != undefined && getAttribute(&#39;rel&#39;) != null)
            {
                var rel = getAttribute('rel');

                //Check whether current element has rel attribute with "Tooltip."
                if (rel.indexOf(sPrefix) >= 0) {
                    var key = rel.split(sPrefix)[1];
                    for (tip in aTooltips) {
                        var str = aTooltips[tip];
                        //Perform a case-sensitive search
                        if (str.search(key) == 0) {
                            var Tooltip = str.split('¦')[1];
                            docElemnts[e].setAttribute('TooltipTitle', Tooltip.split('|')[0]);
                            docElemnts[e].setAttribute('TooltipDescription', Tooltip.split('|')[1]);
                            //Automatically attach mouse over and mouse out event to the Grid Action Button
                            alert(docElemnts[e].onmouseover);
                            docElemnts[e].onmouseover = AttachTooltip;
                            docElemnts[e].onmouseout = function () {
                                hideTooltip('DivTooltip');
                            }
                            break;
                        }
                    }
                }
            }
        }
    }
}
//Attaching event to the current element of the Grid Action Button
function AttachTooltip(e)
 {
     if (!e)
        var e = window.event;
        showTooltip(e, 'DivTooltip', this.getAttribute('TooltipTitle'), this.getAttribute('TooltipDescription'));
}