1. In services.msc, disable and end “Windows Management Instrumentation” (service name “winmgmt”)

    Reason: Used to force Windows Update Installer to use another method than WMI to detect RAM (which in my case was 64 MB)

  2. Uninstall virus scanner (in my case avast!)

    Reason: Virus scanner blocked Windows Update Installer to write to system partition (even when using virus scanner’s “completely disable” feature)