Trying to open a purchased iPod game (Tetris, Sudoku, or Ms. PAC-MAN for example) after playing a built-in game (Vortex, iQuiz, or Klondike) may result in the following message:
"This game cannot be launched. Connect your iPod to iTunes and reinstall the game."
The same issue may occur if you play a purchased game first, then try to open a built-in iPod game.
Reset your iPod before opening a different type of game (built-in or purchased).
To prevent this issue from recurring, use iTunes to update your iPod software to version 1.0.1 or later. See Updating iPod if you need assistance.