ok...let me say something the xbox360 come with 4gb cache in its hard disc...even u del all the video,music and games...its doesnt count 20g...still 16gig...so the cache does keep all the update file or temporary file...if u play too many games (bcoz most game need updates)...and it fullfill the 4g capacity...thats is u have to perform maintainence on ur hard disc to clear the cache (otherwise it'll keep requested for update)- an yes u have to do all the update again ....i cant remember the combo button to perform this maintanence...hmmm...aku pun dapat dari redbull code tu...try tanye redbull or anyone 

but i cant guarantee...sometimes its a symptom to HD failure...happened to merlin b4