Weird Authentication Failures? Could Be That Microsoft Doesn’t Like Duplicate SIDs Anymore

How Dare You Not Use Sysprep!

This recent patch Tuesday added an unexpected new feature to Windows, the enforcement of unique SIDs across systems.  If you dared clone an image onto a second machine on your network, or liked the convenience of using duplicate SIDs to connect via Kerberos or NTLM you have probably had some problems since August 29, 2025.  You will probably see SEC_E_NO_CREDENTIALS errors in Event Viewer or see a few of the errors listed on Bleeping Computer.

Microsoft would like you to stop using duplicate SIDs and suggest setting up those machines from scratch using Sysprep.  If you are not interested in doing so, there is apparently a Group Policy setting which can be deployed to allow you to have machines with duplicate SIDs.  However, there is a catch to that.  You have to reach out to Microsoft support and beg them to give the setting to you as it is not in GPO by default.  This is the third recent authentication error triggered by Microsoft updates, not a tradition we endorse here at PCPer.