Does your printer support multiple paper sizes (I'm guessing yes or why would
you be posting?)
Is it enabled in other applications (MSWord???)?
If you remove the printer driver and reinstall, does that help?
If you remove the printer driver, and get a fresh version from the printer's web
site, does that help?
If you select a different printer, did that help?
(I got nothing if you answer yes or no to these, but you could try a few to see
if you come up with the answer!)