It looks like Microsoft didn't test Windows 8.1 Update's installer thoroughly enough.Windows 8.1 Update, which became available a few hours ago, may in certain circumstances interfere with the proper operation of Windows Server Update Services (WSUS) 3.0 SP2 or WSUS 3.2. Microsoft's recommendation is that you stop deploying Windows 8.1 Update.Microsoft has blocked Windows 8.1 Update from WSUS servers, so it is no longer available for iT admins to distribute to their users. Individuals can still download the update directly through Windows Update.