These specially made GBA cartridges were released to select stores across the UK. Players could visit these stores and connect to a GBA system containing one of these cartridges via link cable to download the patch, as well as receiving a shiny Zigzagoon holding a Liechi Berry. As with the GameCube demo discs, the program does not block fixed games, so the Zigzagoon can be received by the same cartridge multiple times.
It was patch that fixes a glitch and gives you a shiny Zigzagoon holding a Liechi berry, presumably as a consolation prize of sorts.
After the glitch was officially acknowledged by Nintendo and The Pokémon Company, they provided several methods to mitigate the effects of the glitch, and incorporated a permanent fix into later production runs of the game.
The glitch in question was one that was triggered after 366 days have passed after the game has started or the internal battery was replaced, and it caused all calender-based events to be delayed by 366 days.