Same problem here. Sad that Apple eiher doesn't care enough or can't fix this issue. I tried running the updater with Quicktime as suggested and it doesn't work. I have a feeling it is simply hit or miss whether the server is working.
Dear Apple, you should fire the individual responsible. How many potential converts did this cost you?
That is unbelievable embarrasing for Apple... some hundred billion Dollars in cash, but can't afford somebody to fix this small problem!!
A clever guy found the problem for them (DNS issue!), yet MONTHS later Apple hasn't FIXED this crap!
Here's the workaround:
I'm having the very same problem described here. Two more symptoms:
P.S., overriding the DNS lookup by adding an entry to my hosts file as described at https://discussions.apple.com/message/19940078#19940078 worked for me. So this definitely appears to be a server-side issue.
I called Apple about this issue on Wednesday (October 10), and actually managed to get it escalated. Late Friday afternoon (October 12), the rep called me back and said someone was able to duplicate the issue, and it had been sent to the engineers at the appropriate department. As of this evening, my Apple Software Update on a 64 bit Windows 7 install is magically working again.