Windows Update Fails when Installing KB3182373 -- Code 643 Windows Update encountered an unknown error


  • When I try to install KB3182373, a "Security Update for Microsoft Silverlight", Windows Update reports failure with the message "Code 643 Windows Update encountered an unknown error".

    I ran WindowsUpdateDiagnostic.diagcab. It reported that "Troubleshooting couldn't identify the problem".

    What can I do to fix this? I'm running Windows 7 Professional.

    Friday, September 30, 2016 11:43 PM

All replies

  • Hello Pleasejustletmeaskaquestion.

    Download the update from choose the appropriate one according to your Windows 7 version

    Silverlight.exe for 32 bit Windows
    Silverlight_x64.exe for 64 bit Windows

    Execute the installation package as administrator and restart the PC after completing the installation.


    Luigi Bruno

    Monday, October 03, 2016 6:01 PM
  • Hi,

    According to your description, we could boot in Clean Boot and temporarily turn off security software.

    Then try disabling your firewall and updating again. Also we could try manually install the KB by the link Luigi provided.

    According to the error code, it is related to the .NET Framework update installation. We could try follow the steps in the link below to check.

    Hope it will be helpful to you

    Please remember to mark the replies as an answers if they help and unmark them if they provide no help.
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    Tuesday, October 04, 2016 1:30 AM
  • Thank you for the replies. I tried following your suggestions, but nothing has worked so far. Specifically:

    1) I ran Silverlight_x64.exe as an administrator. It said "Installing..." for a few minutes, then said "Installation failed".

    2) I started windows in a clean boot and ran Windows Update. I get the same error as when I run under a normal boot.

    3) I downloaded and ran NetFxRepairTool.exe. It seemed to do its job succesfully, but didn't have any effect on the Windows Update error.

    Does anyone have any other suggestions?

    Tuesday, October 04, 2016 6:48 PM
  • Try resetting Windows Update components: read the Microsoft Knowledge Base article 971058 to know how to do that.


    Luigi Bruno MCP, MCTS, MOS, MTA

    Tuesday, October 04, 2016 6:56 PM
  • Mr. Bruno,

    Thank you for the suggestion. According to Knowledge Base article 971058, the Windows Update components get reset when I run WindowsUpdateDiagnostic.diagcab, and that's the first thing I tried. So, unfortunately, that doesn't fix the problem either.

    At this point, I'm giving up. I've hidden update KB3182373 and I intend to ignore it in the future. I like having a clean up-to-date system, but this is just too much effort.

    Thanks again to everyone for their help.

    Tuesday, October 04, 2016 7:17 PM
  • The last thing you could try could be an in place upgrade, i.e. re-installing Windows 7 over the existing installation: this will replace all the operating system's files with the original ones from the installation support and could solve that problem.
    Read here to know how to perform that operation.


    Luigi Bruno

    Tuesday, October 04, 2016 8:56 PM