One simple thing to try is to make sure that humidity and/or static electricity are not causing the pages to stick together. This has caused multiple pages to feed at once for me a lot of times. Check that the paper is completely dry, especially if the air in the room is particularly humid. Also, in times of cool weather and low humidity, static electricity has more of a tendency to build up. You can thumb through the pages like you would a stack of dollar bills, then try printing again to see if this seperates the pages better.
If none of this works, you might need to have that printer inspected to make sure there are not any parts that have gotten broken or worn.
Hope this helps.
Edit: I stand corrected by the HP Expert cchan (

). Sorry I may have steered you wrong...I only had the best intentions.
