Ha Ha it's XBL end not yours deleting HDD stuff is just a waste of time just sign out and back in (don't even bother rebooting) and that should fix it everyone has this error at some time or another.
If it persists it could even be isp related (at one stage for me it was had to flush my ip addy to fix it!!??!!) again it is nothing to do with your xbox or any content on the HDD.
(The market place file is updated as soon as you connect anyway)