Author Topic: Installed free update 6.0.1125 and now system crash with windows security error  (Read 3352 times)

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  • Guest
Hi,  I installed the Avast update and now I'm getting an error:

An unauthorized change was made to windows
You will no longer receive notifications, including those about your license or activation. Use the link below to find out how to fix your system.
Error 0xC004D401
the security processor reported a system mismatch error.

Learn more online

I got this message yesterday when I turned on my computer after it downloaded the update the night before, and I couldn't do anything but access the internet from that window.  I had to do a system restore.  I turned on my computer this morning, and I see the window again.  Please help!!


  • Guest
If it helps, I thought I had picked up a virus the night before.  But after googling the error, they suggest that some anti-virus software can cause this error & someone else posted on this board that they had the exact same issue with Vista after installing this update.


  • Guest
Re: Installed free update 6.0.1125 and now validation error 0xC004D401
« Reply #2 on: June 13, 2011, 01:02:42 PM »
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:

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.