Javascript function gives NaN in Chrome but woks fine in IE

 function Addvalue() {
        var gv = document.getElementById("<%=Grid_Insert.ClientID %>");
        var gvRowCount = gv.rows.length;
        var total = 0;
        for (i = 1; i < gvRowCount; i++) {
            for (j = 2; j < 15; j++) {
                var a = parseInt(gv.rows[i].cells[j].childNodes[0].value);
                if (j < 14) 
                {
                    if (!isNaN(a))
                     {
                        total = total + parseInt(gv.rows[i].cells[j].childNodes[0].value);
                     }
                }
                if (j == 14) {
                    gv.rows[i].cells[j].innerText = total;
                }
            }
        }
    }
the line 
if (!isNaN(a)) returns true when i Run my page in IE but Retrn false when I run in Chrome..

Pls Help