I've had this problem too with wiiflow and postloader. The only way i've been able to fix it has been to delete the Wiiflow or postloader folder on the SD root. Something in there must lock the games in.
Having issues with Sonic Adventure Battle 2. I get to the progressive scan screen, say yes or no, then it fades to a black screen and doesn't start the game.
Edit: Nevermind, r47 worked