Found the answer - Programs cannot print on 2 pages per sheet. This seems like a driver problem. I would download the updated drivers from HP. Or just get a new printer. I'm just getting a new printer, as this one is on its last legs anyway.
Link: http://h10025.www1.hp.com/ewfrf/wc/softwareCategory?cc=uk&lc=en&dlc=en&product=3811337