Hey Nisreen,

 Do the following as a workaround for your module settings untill this is done properly by dnn:

add to the control  in the directory dnndir\admin\Modules\modulesettings.ascx.cs

the following lines on bindata function:

private void BindData()
        {
            if (Module != null)
            {
                CultureInfo info = new CultureInfo("ar-SA");
                GregorianCalendar calendar = new GregorianCalendar();
                info.DateTimeFormat.Calendar = calendar;
                this.startDatePicker.Culture = info;
                this.endDatePicker.Culture = info;

etc...

And the error will cease to appear. You can also set the calendar to "HijriCalendar" instead of the "GregorianCalendar" object but the support for hijri is not available for raddatepicker as i noticed.

Take care.