Either because you cheated and did not get the national pokedex or you have already migrated for that day. But probably cause you cheated.
Chat with our AI personalities
Get a Deoxys in Pokemon Emerald, Ruby, Sapphire, Firered, or Leafgreen using the Mystery Gift, and migrate it to your Diamond Version.
No you must migrate a charizard from firered or leafgreen.
You don't. That is only in Emerald version.
Nope. You may not migrate pokemon from US games or link them with other region games, in your case UK PAL
lol u cant its only in diamond and pearl