Make sure your printer is selected in the Print window (Windows) or in the Page Setup and Print windows (Mac OS X).
Your document may have more pages than you think. Select Print Preview from your application’s File menu before printing. Then either select to print only the current page, or only those pages with text, or delete the extra pages in your document before printing.
Paper settings in the printer software may be incorrect for your paper size. Check the paper size, orientation, printable area, and layout settings to make sure they’re correct for your paper size.
If these suggestions don’t help, the print head nozzles may be clogged.
and then there's my wacky suggestion, jumping off from Epson's suggestion that you have a multi-page document:
Are you really sure you're printing the exact same file, the exact same way (with supposedly only paper size being different)? Could it possibly be that you have a multi-layered document, and you're printing a "blank" layer? If your doc is jpg or is a psd that has been flattened, my theory is bogus.
I only mention it because I have done this, "printed" a blank layer.