The Halo series has always been about addictive multiplayer experiences, so it's most disturbing to find out that campaign co-op gaming on the latest title is a non-starter for people without a hard drive attached to their 360. An issue has been identified by users of the 4GB Xbox 360, whereby attempts to team up on the baddies with your buddies -- whether locally or via Xbox Live -- is met with an error message saying that a HDD is "required for this game type." This affects both Halo: Reach and the earlier Halo: ODST. Adding extra memory via USB has been found to be ineffective, but at least Microsoft has stated that it's aware of the limitation and is "quickly working to resolve it." Standard multiplayer is predictably unaffected, so we suggest taking your rage out on some newbies while the MS techs figure out their caching algorithms.