Grey means that you can't edit that part, taken from that I could tell you're using the storage codes. Three possibilities I could think of:
- You're using different region game cart and pokesav
- If you typed in manually through touch screen, you might have typed something wrong
- For the Box and Slot you chose for Empoleon to be. You have to have a pokemon there to be replaced. If there's no pokemon ready for replacement, the code won't take effect.