Glitched: Bejeweled 2
Achievement: One of Puzzle, Action, Classic, Endless
Description: Bejeweled 2 has 4 main modes (Puzzle, Action, Classic, Endless) and an achievement for each. When you reach the requirements for the 4th mode, you should unlock both MultiMode and the expected mode achievement. However, some people only unlock MultiMode.
The other achievement might then be permanently unattainable. I've never read a post by someone who had the glitch happen, then later got the missing achievement.
If you haven't unlocked MultiMode yet: Each Bejeweled 2 achievement has a Congratulations splash screen. It has been suggested that you do not dismiss the screen until both MultiMode and the other achievement pops. You may have to wait several seconds.
Here's a thread about the glitch: