For those that can't figure out how to evolve or don't want to read the guides on this site for whatever reason...
Evolution in this game is different from Battle Spirit 1, assuming you've played that one already. In this game, there are essentially two types of evolution. The first involves filling that meter at the top all the way. When you have done so, pressing A+B will surround your character's mid section with Digicode. As long as that Digicode is around your character, and as long as the meter at the top is still blue, you will be able to slide evolve to your Beast Form whenever you attack. That is, your special attacks are temporarily replaced by your Beast Spirit's attack.
The second type of evolution occurs when you've obtained 5 of those crystals that occasionally fall out of you, your enemy, or the background Digimon that can be attacked. Pressing Up and A+B will let your character perform an animation. If your enemy is caught in the range of your animation, you will initiate a short scene in which your character summons his/her Ancient Spirit. The Ancient Spirit attacks the enemy, and you get multiple 3 point orbs.
....and there you go. As for that other user's problem, I assume you obtained a bootleg copy of the game. That would be one of the possible explanations for a game not keeping your achievements.
Yes, this is all old'd, but I just got to these here seemingly empty boards, so yeah. Perhaps I'll aim for a Wonderswan and get the 3 Battle Spirits on that handheld! =D
Good to see this topic finally posted. Hope to see a sticky of it go through.
If you believe in Jesus Christ and are 100% proud of it put this as your signature.
(~G) State Alchemist of the OVERlords. ***~Official OVERlord Seal~***