I HAVE THE SAME PROBLEM WITH CODE ERROR 646. I DON'T KNOW WHAT TO DO? MY DESKTOP IS RUNNING ON WINDOWS 7.

Try this first: http://support.microsoft.com/kb/2258121 If that doesn't do the trick then go through this: http://social.answers.microsoft.com/Forums/en-US/vistawu/thread/6e716883-7af4-4a9f-8665-2f4dd57eee8d

Hi, If it is a Windows Update issue, you can go to Windows Update history to see which update failed to be installed, go to Windows Download Center to download its package and install it manually. Meanwhile, as it is a Windows 7 related issue, it is recommended to post on Windows 7 forum: Windows 7 Forums http://social.answers.microsoft.com/Forums/en-US/category/windows7 Windows 7 IT Pro http://social.technet.microsoft.com/Forums/en/category/w7itpro Shaon Shan| TechNet Subscriber Support in forum| If you have any feedback on our support, please contact tngfb@microsoft.com