I got this too once when, instead of trading directly an egg over, I placed it directly in a box from my pearl save to heartgold. I found that fixing it is to change the place where you meet it at '2002' to say "Egg Obtained" instead of "Egg Received". I found it unsightly so I adjusted it accordingly. If you made the egg, make sure to indicate where it came from as well, "Day Care Couple"; I found that when it does hatch after being 'traded', it will just be replaced to where it actually hatched at.