Grazie per la risposta.
Ho provato in entrambi i modi ma non va.

codice:
	$('.form_date').datetimepicker({
        language:  'fr',
        weekStart: 1,
        todayBtn:  1,
		autoclose: 1,
		todayHighlight: 1,
		startView: 2,
		minView: 2,
		forceParse: 0,
		startDate: today,
		formatDate: 'Y-m-d',
		disabledDates: ['2016-04-29']
    });
oppure

codice:
	$('.form_date').datetimepicker({
        language:  'fr',
        weekStart: 1,
        todayBtn:  1,
		autoclose: 1,
		todayHighlight: 1,
		startView: 2,
		minView: 2,
		forceParse: 0,
		startDate: today,
		disabledDates: ['2016/04/29']
    });