DatePicker.setMinDate(long minDate) throws IllegalArgumentException: Time not between

I have a time interval consisting of a beginning and an end date. I have a way of letting the user set these dates through DatePickerDialogs. Here is the code of the method that creates and shows the dialogs:

private void editInterval(boolean beginning) {
    DatePickerDialog dpd;
    Calendar cal = Calendar.getInstance();
    if (beginning) {
        dpd = new DatePickerDialog(this, new DatePickerDialog.OnDateSetListener() {             
            @Override
            public void onDateSet(DatePicker view, int year, int monthOfYear, int dayOfMonth) {
                someTimeDuringYear1 = year;
                someTimeDuringMonth1 = monthOfYear + 1;
                someTimeDuringDay1 = dayOfMonth;
                Calendar cal1 = Calendar.getInstance();
                cal1.set(Calendar.YEAR, year);
                cal1.set(Calendar.MONTH, monthOfYear);
                cal1.set(Calendar.DAY_OF_MONTH, dayOfMonth);
                Calendar cal2 = Calendar.getInstance();
                cal2.set(Calendar.YEAR, someTimeDuringYear2);
                cal2.set(Calendar.MONTH, someTimeDuringMonth2);
                cal2.set(Calendar.DAY_OF_MONTH, someTimeDuringDay2);
                if (cal1.getTimeInMillis() > cal2.getTimeInMillis()) {
                    someTimeDuringYear2 = someTimeDuringYear1;
                    someTimeDuringMonth2 = someTimeDuringMonth1;
                    someTimeDuringDay2 = someTimeDuringDay1;
                }
                updateSomeTimeDuring();
                editDepartureInterval();
            }
        }, someTimeDuringYear1, someTimeDuringMonth1 - 1, someTimeDuringDay1);
        dpd.setTitle(getString(R.string.beginning_of_interval));
        cal.add(Calendar.MONTH, 6);
        dpd.getDatePicker().setMaxDate(cal.getTimeInMillis());
        cal.add(Calendar.MONTH, -6);
        cal.add(Calendar.DATE, 2);
        dpd.getDatePicker().setMinDate(cal.getTimeInMillis());
    } else {
        dpd = new DatePickerDialog