OK, I cannot figure out what has happened, but the same thing is going on with my girlfriends macbook as well. Software update is not working. Everytime I try to run it, it takes like 2 seconds, then goes to the software update screen and says Updates are ready to be installed blah blah blah... But there are no updates listed!! I found some directions on here saying to go to Library -> caches -> apple.com.softwareupdate ... and delete. I have done this but this did not fix the problem?? Any ideas?