Are you among one who own a copy of Halo: Reach and want to play some cooperatively camapign on your 4GB Xbox 360, than we are sorry to say that you can't do it for a while.
As gamers attempting to play cooperatively campaign of Halo: Reach on 4GB Xbox 360 are welcome with a message that, One or more players do not have the hard drive required for this game type. Apart from this issue it is said that USB memory doesn't appear to work either.
But according to Microsoft the issues temporary and they have already started their work on developing a fix for the same to resolve it. Here is what a spokeperson commented on the issue:
"We are aware of the issue and are quickly working to resolve it,".