I just finished up the EV training on my Nincada and I was leveling it up so that it could evolve into Ninjask to use for the Elite Four fights, but when it reached level 20 and evolved, the game crashed. I tried resetting and retrying several times, but the outcome remained the same.
This is the error that I received when the game crashed.
I dont know if this will work but try evolving it with your party full. Since nincada evolves into ninjask and shedninja, the shedninja generated might be crashing the game and if you had a full party when your game crashed try taking a pokemon out just in case it is the game trying to find a place to put he shedninja that crashes it