SNK Playmore's SNK vs. Capcom Card Fighters DS game for Nintendo DS (only in America) that had a game-halting bug that kept you from collecting all the cards. It's fixed now, but if you have an (April 24) launch game with the bug you can get your copy replaced.
To clarify if you don't know if you have a buggy version: The bug occurs on the ninth floor of the tower during the second play through. The game crashes after talking to an opponent named Jon. Fighting him is necessary to complete the game, so you're stuck at that point.