need an ar code for white 2

Yes, the best solution to solving your cheating problem, when not using any allow you to play perfectly fine, is by not cheating. There...problem solved.

 

Try not using the pre-patched rom. The prepatched rom contain anti piracy fix and no experience fix. But knowing you are on M3, then likely you must use pre-patched rom otherwise rom will not load properly. Another way around is to just use 1 cheat code at a time. Too many cheats on can also contribute to your problem. Because cheats basically are offsets used to alter the rom's internal offset to meet the purpose of the cheat intended. Thus that can play a contributing factor in causing the problem you had encountered before.

Another way around is, to load your Save File to POKEGEN, and add items to your poke bag, then use it to help speed up your pokemon's experience. It's the safest cheating method.

edit:

or, since you're on M3 Real, means it can use YSMENU/TTMENU as secondary firmware, thus enable you to run clean/unpatched rom.
That way, you can use cheats without too much worry.

 

Place the usrcheat.dat inside the TTMENU folder, you'll see the option to activate the cheat just before you load the rom to play after double click on ttmenu.nds or ysmenu.nds.

 

If you are already running the ttmenu.nds or ysmenu.nds, make sure to use clean-unpatched rom.
Try to remove your pokemon save file to your pc. Then re-try playing the game. If it work, most likely your save file been corrupted when you had that earlier problem. If problem stay, try not activating the cheat, if it work, then likely there's a cheat code that is faulty.
Other than that, you could try using a better SD Micro such as Sandisk brand, sometimes SD Micro quality may have effect. Other than that, I'm lost of words. Cause it should have work well since RGF's YSMENU supports M3 Real.