AirPrint & Epson

I have a Epson XP-640 and when I try to use AirPrint from iPad the only paper size I can chose is A4. I have been using 8.5X11 paper. It will print about 1/2 the time and then I get "incorrect paper size. Load correct paper size" message. Epson says it is a AirPrint problem. All softwares are up to date. Is it a apple problem or ?