I'm having trouble identifying your exact problem, but here are some things you should consider:
1) Wake up the pokemon, then tuck him in again. (You've probably already tried this)
2) Tuck in a different pokemon (You've probably done this too, and even though it's rare to find a pokemon that doesn't work in the dream world, it's still a possibility)
3) You could wait a few days, then try game sync again, and see if your pokemon is in the Dream World.
4) If at all possible, you could try tucking in a pokemon using a different DS.
5) Also, (if possible) you could use a different game-card to tuck in your pokemon.
For more help and information on the dream world, you can visit the following sites:
There are also some walkthroughs and guides on youtube.
If all else fails, you may have to create another account.