Nintendo’s official word on the matter is that:

Unfortunately we have discovered that a small number of games contain the wrong version of the disk due to an assembly error. We have therefore decided to recall all copies of the game from UK retailers so that this mistake can be corrected.

We will re-launch Mario Party 8 in the UK as soon as possible and will announce a new launch date shortly. We very much regret any inconvenience caused.

Although the game was originally due out last month, a manufacturing error delayed the game a week (until today). What has happened with the production line I wonder? I hope they fix it in time for more anticipated releases later on in the year.