function _togglePrevNext(bSkipMonthCheck){

		var oDate = new UniversalDate(_getStartDate.call(this).getTime());
		var iItems = this._getItems();
		var iYear = oDate.getJSDate().getUTCFullYear();
		var iYearMax = this._oMaxDate.getJSDate().getUTCFullYear();
		var iYearMin = this._oMinDate.getJSDate().getUTCFullYear();
		var iMonth = oDate.getJSDate().getUTCMonth();
		var iMonthMax = this._oMaxDate.getJSDate().getUTCMonth();
		var iMonthMin = this._oMinDate.getJSDate().getUTCMonth();
		var iDate = oDate.getJSDate().getUTCDate();
		var iDateMax = this._oMaxDate.getJSDate().getUTCDate();
		var iDateMin = this._oMinDate.getJSDate().getUTCDate();
		var iHours = oDate.getJSDate().getUTCHours();
		var iHoursMax = this._oMaxDate.getJSDate().getUTCHours();
		var iHoursMin = this._oMinDate.getJSDate().getUTCHours();
		var iMinutes = oDate.getJSDate().getUTCMinutes();
		var iMinutesMax = this._oMaxDate.getJSDate().getUTCMinutes();
		var iMinutesMin = this._oMinDate.getJSDate().getUTCMinutes();
		var oHeader = this.getAggregation("header");

		if (this._iMode == 2 && !bSkipMonthCheck) {
			// in line month picker don't disable buttons
			var oMonthPicker = this._getMonthPicker();
			var iMonths = oMonthPicker.getMonths();
			var iStartMonth = oMonthPicker.getStartMonth();
			var iEndMonth = iStartMonth + iMonths - 1;

			if (iStartMonth == 0 || (iYear == iYearMin && iStartMonth <= iMonthMin)) {
				oHeader.setEnabledPrevious(false);
			} else {
				oHeader.setEnabledPrevious(true);
			}

			if (iEndMonth > 10 || (iYear == iYearMax && iEndMonth >= iMonthMax)) {
				oHeader.setEnabledNext(false);
			} else {
				oHeader.setEnabledNext(true);
			}

			return;
		}

		if ((iYear < iYearMin ||
				(iYear == iYearMin && ( bSkipMonthCheck || ( iMonth < iMonthMin ||
						(iMonth == iMonthMin && (iDate < iDateMin ||
								(iDate == iDateMin && (iHours < iHoursMin ||
										(iHours == iHoursMin && iMinutes <= iMinutesMin)))))))))
				|| ((this._iMode == 1 || this._iMode == 2) && this.getPickerPopup())) {
			oHeader.setEnabledPrevious(false);
		} else  {
			oHeader.setEnabledPrevious(true);
		}

		oDate.setUTCMinutes(oDate.getUTCMinutes() + (iItems) * this.getIntervalMinutes() - 1);
		iYear = oDate.getJSDate().getUTCFullYear();
		iMonth = oDate.getJSDate().getUTCMonth();
		iDate = oDate.getJSDate().getUTCDate();
		iHours = oDate.getJSDate().getUTCHours();
		iMinutes = oDate.getJSDate().getUTCMinutes();
		if ((iYear > iYearMax ||
				(iYear == iYearMax && ( !bSkipMonthCheck || ( iMonth > iMonthMax ||
						(iMonth == iMonthMax && (iDate > iDateMax ||
								(iDate == iDateMax && (iHours > iHoursMax ||
										(iHours == iHoursMax && iMinutes >= iMinutesMax)))))))))
				|| ((this._iMode == 1 || this._iMode == 2) && this.getPickerPopup())) {
			oHeader.setEnabledNext(false);
		} else  {
			oHeader.setEnabledNext(true);
		}

		if (this._iMode === 1) {
			var oLastDayOfMonth = new UniversalDate(oDate.getTime());
			oLastDayOfMonth.setUTCDate(1);
			oLastDayOfMonth.setUTCMonth(oLastDayOfMonth.getUTCMonth() + 1);
			oLastDayOfMonth.setUTCDate(0);
			var iDays = this.getAggregation("datesRow").getDays();
			oDate.setUTCDate( 1 + (Math.ceil(oDate.getUTCDate() / iDays) - 1) * iDays );
			if (oLastDayOfMonth.getUTCDate() - oDate.getUTCDate() < iDays) {
				oDate.setUTCDate(oLastDayOfMonth.getUTCDate() - iDays + 1);
			}
			iDate = oDate.getUTCDate();
			if (iDate <= 1 || (iYear == iYearMin && iMonth == iMonthMin && iDate <= iDateMin)) {
				oHeader.setEnabledPrevious(false);
			} else {
				oHeader.setEnabledPrevious(true);
			}

			if ((iDate + iDays) >= oLastDayOfMonth.getUTCDate() || (iYear == iYearMax && iMonth == iMonthMax && iDate >= iDateMax)) {
				oHeader.setEnabledNext(false);
			} else {
				oHeader.setEnabledNext(true);
			}
		}

	}
Enables / Disables previous and next button in the Header.
This function assumes there is a "monthPicker" aggregation unless the bSkipMonthCheck flag is false.
So callers must take care.
@param {boolean} bSkipMonthCheck if month picker should be examined or not
@returns {void}
@private