Yesterday's launch of Halo: Reach has been marred slightly for owners of the 4GB edition of the new Xbox 360 Slim, who reportedly can't use the game's co-operative play functions. Gaming site Nukezilla was one of the first to notice that Bungie's newly-released first-person shooter presents an error message when players try to start a co-operative game on the cheaper Xbox 360 Slim models, which include 4GB of internal flash memory. "One or more players do not have an Xbox 360 Hard Drive," the error reads. "An Xbox 360 Hard Drive is required to play co-op on Xbox LIVE or system link." Other multiplayer modes do not seem to be affected by this error. A Microsoft representative told Gamespot they "are aware of the issue and are quickly working to resolve it." In the meantime, the only option for 4GB Slim owners that want to play co-operative Halo: Reach seems to be purchasing a hard drive from Microsoft. Microsoft's official Halo: Reach frequently asked questions page notes that "some multiplayer aspects of Halo: Reach require an Xbox 360 certified hard drive." While the flash memory inside the 4GB Slim model is not technically a hard drive, the two storage types are used interchangeably by most Xbox 360 games. Posters on Bungie's official forums have noted similar problems playing Halo: ODST as recently as August. First released in the U.S. on August 3rd for $199, the 4GB Slim model serves as a replacement for Microsoft's previous Xbox 360 Arcade unit, which had less than 1GB of built-in memory.