scheduler.templates.week_date_class and minicalendar

Hi

I change my scheduler.templates.week_date_class like this:
scheduler.templates.week_date_class = function (date, today) {
if(isFreeDay){
spanWork=scheduler.addMarkedTimespan({
days: date.getDay(),
zones: [“420”,“1260”],
css: “not_work_hours”
});
}
}
Where isFreeDay is a boolean variable that i manage
It works fine but if i use the minicalendar the code inside the if statement give an error and the minicalendar handler doesn’t work
Where is the problem?

the css not_work_hours:
.not_work_hours {
background-color:#A9A9A9;
opacity:0.55;
filter:alpha(opacity=55);
cursor: pointer;
z-index: 0;
}

It’s possibile that the problems are opacity and filter?

debugging i see that the problem it’s for ie < 9 and only if sunday is marked with background-color opaque