sender._days.all.length gives results as undefined in mozilla and Chrome browsers, where as its working good in IE

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Javascript

while i am writing the javascript code, it shows the result the undefined in mozilla and chrome browsers, please see below my code as

Here sender._days.all.length returns undefined in mozilla and chrome browsers,but it's working good in IE, Can any one have solution or alternate solutions for this problem

This Control belongs to AjaxToolkit

<ajaxToolkit:CalendarFutureExtender ID="clnDtDesired"  runat="server" Format="MM/dd/yy"
    TargetControlID="dtDateServiceDesired" PopupButtonID="imgDtServiceDesired"  
    önClientShown="DisableWeekends"/>
 <asp:Label ID="lblreqDtDesired" Width="5" Text="*" runat="server" ForeColor="red"
    CssClass="lbl">

function  DisableWeekends(sender, args)
{
    alert(sender._days.all);
    debugger;
    for(var i=0; i<sender._days.all.length;>        {
        for(var j=0; j<6; j++)
        {
            if(sender._days.all[i].id == "clnDtDesired_day_"+ j +"_0")
            {
                sender._days.all[i].disabled = true;
                sender._days.all[i].innerHTML = "<div>"+sender._days.all[i].innerText+ "</div>";
            }
            if(sender._days.all[i].id == "clnDtDesired_day_"+ j +"_6")
            {
                sender._days.all[i].disabled = true;
                sender._days.all[i].innerHTML = "<div>"+sender._days.all[i].innerText+ "</div>";
            }
        }
    }
}

Thanks
Viswanath J