Thank you so much!!! I got it working by changing the code to this...
function getWeekSelect($name, $selectedWeek, $selectedYear, $deep, $attribs = '')
    {
    	$arr = array();
		for ($i = 0; $i <= $deep; $i ++) {
			$date = JFactory::getDate('+ ' . $i . ' week');
			$date->modify('this week');
			
			$week = (int) $date->format('W');
			$week1 = $date->format("n/j");
			//in php 5.2 retur null, in php 5.3 return DateTime Object
			$date->modify('+6 days');
			$week2 = $date->format("n/j");
			$year = (int) $date->format('Y');
			$text = $week .'/'.$year.' ('.$week1 . ' - ' . $week2.')';
			$arr[] = JHTML::_('select.option', $week . ',' . $year, $text);
		}
        return JHTML::_('select.genericlist', $arr, $name, $attribs, 'value', 'text', $selectedWeek . ',' . $selectedYear);
    }