var alertMessage;
function validateCheckBoxes(name)
{
    var obj = document.getElementsByName(name);
    if(obj!=null&&obj!=undefined)
    {
        for(var i=0; i< obj.length; i++)
        {
            if(obj[i].checked)//return first record found.
            {
                return true;
            }
        }
    }
    alert(alertMessage);
    return false;
}