function openCalendar(DateField_ID)
{
	// position the popup relative to parent window
	var posX;
	var posY;

	if (window.screenX) { // Mozilla
		posX = "screenX=" + (window.screenX + 230);
		posY = "screenY=" + (window.screenY + 20);// 200
	} else { // IE
		posX = "left=" + (window.screenLeft + 230);
		posY = "top=" + (window.screenTop - 70);// 200
	}

	var windowOptions = posX + "," + posY
                            + ",width=365,height=250"
                            + ",toolbar=no,location=no,directories=no,status=no,menubar=no"
	                        + ",resizable=no,copyhistory=yes,scrollbars=no";

	var adr =  'tick_sel_calendar.aspx?DateField_ID=' + DateField_ID;

        // The code below makes sure only one calendar window will open.
        // If it is hidden by other windows, put it back on top.
	    if (!window.winTickselCalendar) 
	    {
	        window.winTickselCalendar = window.open(adr, "Select date arrival", windowOptions);
	    } 
	    else 
	    {
	        if (window.winTickselCalendar.closed) 
	        {
	            window.winTickselCalendar = window.open(adr, "Select date arrival", windowOptions);
	            window.winTickselCalendar.focus();
	        } 
	        else 
	        {
	            window.winTickselCalendar.location.href = adr;
	            window.winTickselCalendar.focus();
	        }
	    }
	    
}