Halo ReachGamers who thought they were making a smart move by picking up Microsoft’s entry-level Xbox 360, which retails for $199 and comes with 4GB of memory, faced a nasty dose of reality yesterday when they found themselves unable to access Halo: Reach’s online co-op mode, Kotaku reports.

Those who attempt to play a co-op session, which allows them to play through levels with their online friends, receive an error message saying that the game requires a hard drive for that mode. Other online modes like “versus” deathmatches work just fine.

Following gamer complaints, Microsoft updated its support entry for Halo: Reach with this message: “One or more players do not have a certified Xbox 360 hard drive attached to their Xbox 360 console. Some multiplayer aspects of Halo: Reach require an Xbox 360 certified hard drive.”

The issue brings to light Microsoft’s resistance to make the Xbox 360’s hard drive a required component, instead of an optional one. Many had expected the company to offer an inexpensive version of the console with a small hard drive, but instead it opted for cheaper flash memory. And while the company did throw gamers a bone by letting them use standard USB flash drives as storage for the console, using flash drives apparently doesn’t resolve this Halo: Reach issue.

Gamers can fix the issue by picking up a separate Xbox 360 hard drive — but with a retail price of $129, they would have been better off purchasing the $299 version of the console which includes the 250GB hard drive.

Alternatively, 4GB Xbox 360 owners can wait and see if Microsoft manages to resolve the issue. Eurogamer reports that the company is working on a fix, but there’s no telling when that will be released.