Newly introduced security measures cause login problems on Windows 11 systems with duplicate security IDs (SIDs).
Since late August, users have been experiencing login issues on Windows 11 and Windows Server 2025. According to Microsoft, this is due to new security measures disrupting authentication protocols when devices contain duplicate Security IDs (SIDs).
Issues Following Recent Updates
The error occurs after installing update KB5064081 (released August 29) or KB5065426 (September 9). Users report being prompted multiple times for login credentials, unable to access shared network folders, or experiencing non-functional Remote Desktop connections. Microsoft states that error messages are also being logged in Event Viewer, even when valid login credentials are used.
Unique SIDs
Microsoft confirms that the issues can only be resolved by rebuilding affected devices with duplicate SIDs to ensure each SID is unique. The company refers users to their support page.
Although the updates were intended to strengthen authentication security, they are actually causing problems with protocols. Administrators are advised to check their Windows 11 systems for duplicate SIDs before installing these security updates.