Hi!
I'm experiencing the exact same problem as described here.
In my main account, after launching Software Update, the progress bar disappears after a while and the main window displays a "New software is available for your computer." (although I know there is not, since I've run the Software Update from another admin account and it says it's up to date) and the part of the window that should display the list of updates is empty and the "Install" button at the bottom right is greyed out.
If I go to "Preferences…", I can see, below the "Check Now" button, the following text : "Last attempt: Failed. Error occurred while checking."
I've, of course tried the procedure that worked for "curlz813" (see this thread :
http://discussions.apple.com/thread.jspa?messageID=6727973) several times, without any luck.
The same behaviour continues.
The strange thing is that on my wife's account (also an admin account), the Software Update goes on well and says it's up to date.
What can I do ?
Thanks in advance for any help.