I also have the very same type of Error: 0xC004D401 somewhat soon after 6.0.11xx and that has crippled my Vista operating system since it now thinks it is not legal. A lot of functions were then deliberately disabled by Vista. I will not reboot since I don’t want to end up losing whatever functionality I have in this session.

Microsoft has user discussion forums for VISTA validation at:

http://social.microsoft.com/Forums/en-US/genuinevista/threads

The thread name is “Note to users of Avast! v6 Anti-Virus” and a lot of VISTA/AVAST users have noted similar problems with Avast 6 on VISTA (typically with Service Pack 1). The current dominant advice so far is to uninstall whatever software was causing the problem until the problem with compatibility was fixed. Unfortunately that means Avast. Of course, if the problem isn’t fixed, Service Pack 2 cannot be installed without uninstalling Avast also.