jquery奇怪的有关问题（按钮禁用启用）

///我这里直接禁用了button <asp:ImageButton ID="imgbtnClear" runat="server"                      ImageUrl="~/image/shouye/qinkong.png" onclick="imgbtnClear_Click"  Enabled="false"/>js:从网上下载的插件$(function(){jQuery.fn.countDown = function(settings) {            var cd=new Date();            var td=new Date(settings.startDate);                    var displayText="";                //开始构造显示用的字串                var secondDiff=cd.dateDiff("s",td);                var dayDiff=parseInt(secondDiff/(60*60*24));        displayText+=(dayDiff>=0?dayDiff:"0")+"天 ";                var hourDiff=parseInt(secondDiff/(60*60));        displayText+=(hourDiff>=0?hourDiff%24:"0")+"小时 ";                var minuterDiff=parseInt(secondDiff/(60));        displayText+=(minuterDiff>=0?minuterDiff%60:"0")+"分 ";                        displayText+=(secondDiff>=0?secondDiff%60:"0")+"秒";        $(this).text(displayText).animate({"none":"none"},settings.duration,'',function() {        if(secondDiff>=0) {//在这里，如果时间大于0，则启用按钮（难道我这个移除禁用按钮的代码写错了？？？求各位大神赐教）        jQuery("#btnTouzhu").removeAttr("disabled");            $(this).countDown(settings);                    }else{//如果时间小于等于0，按钮失效，这里可以            $("#imgTouzhu").attr({src:"../../image/shouye/ddkj.gif"});            $("#imgTouzhu").attr({"disabled":"disabled"});            settings.callBack(this);        }            });            return this;};