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.
More from the WSUS Product Team blog on TechNet:
There is a known issue that causes some PCs updated with the Windows 8.1 Update to stop scanning against Windows Server Update Services 3.0 Service Pack 2 (WSUS 3.0 SP2 or WSUS 3.2) servers that are configured to use SSL and have not enabled TLS 1.2. ... Microsoft plans to issue an update as soon as possible that will correct the issue and restore the proper behavior for Windows 8.1 Update scanning against all supported WSUS configurations. Until that time, we are temporarily suspending the distribution of the Windows 8.1 Update to WSUS servers. ... You may still obtain the Windows 8.1 Update from the Windows Update Catalog or MSDN. However, we recommend that you suspend deployment of this update in your organization until we release the update that resolves this issue.
The problem affected WSUS 3.2 running on Windows Server 2003 SP2, Windows Server 2003 R2 SP2, Windows Server 2008 SP2, and Windows Server 2008 R2 SP1 when HTTPS and SSL were enabled but TLS 1.2 was not. Microsoft also proposed a workaround for PCs that had already been updated to Windows 8.1 Update 1 through WSUS: Enable TLS 1.2 or disable HTTPS. Doing so will let PCs deploy future updates from WSUS.
Separately, the MSDN version of Window 8.1 Update needs an additional update, KB 2934018.
This story, "Microsoft removes Windows 8.1 Update from WSUS update servers," was originally published at InfoWorld.com. Get the first word on what the important tech news really means with the InfoWorld Tech Watch blog. For the latest developments in business technology news, follow InfoWorld.com on Twitter.