Secret Area - Solution
The secret area is indeed in level 43. When you start, head straight up and open the door and slam into the right wall (I have no idea why, but that's what it requires)
Now go back down, and to the left a wall that was once there should be gone. Head to the left (don't go too high, there are invisible walls) and you will hit a switch. Hit it and turn back around. Complete the level, but don't get all 7 sun beans. When you are at the end, go through the red exit area and in the top right there is a double wall, one there and one missing. Just ram into the top-right wall behind the missing wall and it will take you to the hidden level and unlock the achievement.
Thanks to everyone on the board who figured out what level this was in and that you can go through the red exit. NOTE: I was doing this on tilt mode, not sure if it works on touch mode as well.
Last edited by tylerh1701; 12-15-2011 at 04:58 AM.