Themasterriolu

So, I was grinding a Larvitar I got from someone to Level 45, and It learned crunch. I deleted one of the moves it had, only for it to immediately be replaced by taunt. This is probably because I tried seeing if it was a good move for Larv before, but it wasn't. So I went to go relearn it via the move relearner, and I try buying crunch for 2,000 pokedollars, but it doesn't ask me what move I want to replace for Crunch to be relearned. I tried again, and the same thing happened. Because of this error, I can't learn Crunch. Am I the only one that's had this happen?