KB5131090: slmgr /rearm breaks Citrix MCS image prep

Call: Known issue. After November’s Windows Server updates, slmgr /rearm is failing for some people, and that takes Citrix Machine Creation Services image prep down with it. This was reported, not confirmed: three people in the r/sysadmin Patch Tuesday megathread at first, eight by Wednesday evening. Deploy to session hosts if you like. Don’t patch your MCS master images until you’ve tested a prep.

Update, Nov 12: No fix yet. Microsoft still says a resolution “will be available in the coming days,” and no out-of-band update has shipped. The activation known issue now also appears on the Windows 10 page (KB5131096 (opens in a new tab), added Nov 11) with the same wording, so it isn’t only a Server problem. According to admins quoting Microsoft’s admin-center notice, it also covers Windows 11 23H2 (KB5131087). The public wording hasn’t changed: 0x80041008 on slmgr.vbs /skms-domain and /ipk, already-activated devices stay activated, and the workaround comes through Microsoft Support for business. It still says nothing about /rearm or Citrix MCS. The r/sysadmin megathread is up to about 15 separate reporters, from eight on Wednesday evening, and several of them mention /rearm and MCS. One says their Citrix MCS master-image rollout is blocked. We still haven’t seen a Citrix notice. The call doesn’t change: leave November off MCS master images until you’ve run a test prep or Microsoft ships the fix.

Update, Nov 11 evening: Microsoft now lists a related known issue on the November Server KB pages (KB5131090 (opens in a new tab) for 2022, KB5131085 (opens in a new tab) for 2019, KB5131080 (opens in a new tab) for 2025). In its words, “certain Windows activation and licensing operations performed using the Software Licensing Management Tool might fail” with error 0x80041008, “Invalid parameter (SWbemObjectEx).” The commands it names are slmgr.vbs /skms-domain and slmgr.vbs /ipk. It doesn’t mention /rearm or Citrix MCS, so we can’t say Microsoft has confirmed this exact failure. It may well be the same bug, but we can’t tell from outside. If you set KMS hosts or install keys with slmgr during builds, though, this hits you whether or not you use Citrix. Microsoft says already-activated machines stay activated, offers a workaround through Microsoft Support for business, and expects a fix “in the coming days.” The megathread is now up to eight separate reporters, including Server 2025 master images. One rolled back to the October CU. Another says a Citrix case suggested Citrix had only just been told about it. We haven’t found a Citrix notice. The call stays the same.

What breaks: MCS image preparation fails at the rearm step. The error one admin quotes: “During image preparation, the rearming process for the copy of Windows installed on the master image failed.” A new catalog or an image update won’t go out, and you find out at the worst possible moment, which is during the maintenance window.

Who’s hit: Citrix MCS shops building images on Windows Server. Reports cover Server 2019, 2022 and 2025 master images, and one names KB5131090. One admin says Windows 11 25H2 VDAs are fine. We haven’t seen it outside Citrix, but anything else that rearms a master image is worth checking.

Workaround: Microsoft has a workaround for the 0x80041008 activation issue, but you have to get it through Microsoft Support for business. If image builds are blocked, open the case now.

Hold November’s Server CUs (KB5131090 on 2022, KB5131085 on 2019, KB5131080 on 2025) on MCS master images until you’ve done a test prep with them installed.
If a master already has the update and prep fails, roll back to a snapshot from before it, or uninstall the CU on the master and run the prep again.
Keep patching the running VDAs and everything else. This is an image-build problem, not a running-server one.

We’ll update this when Microsoft ships the fix or Citrix says something.

Sources: r/sysadmin November megathread (opens in a new tab), Server 2022 release health (opens in a new tab), Server 2019 release health (opens in a new tab), KB5131090 (opens in a new tab), KB5131085 (opens in a new tab), KB5131080 (opens in a new tab).

KB5131090: slmgr /rearm breaks Citrix MCS image prep

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