Users report that the optional Windows 11 update KB5124010, released on September 23, causes system instability. The issue specifically affects users running versions 26100.9550 and 26200.9550 of Windows 11 24H2 and 25H2.
The crash is triggered when multiple MP3 files are played simultaneously. Technical analysis points to a failure in the msmpeg2ac3dec.dll audio decoding component, located in the System32 and SysWOW64 directories.
The presence of the problematic file depends on the installation history. Systems upgraded from Windows 11 22H2 retain the file, while clean installations of 24H2 or 25H2 do not include it and remain unaffected.
The bug impacts legacy software and enterprise applications. Users report crashes in games such as SimCity 4 and Fallout: New Vegas, as well as in the myApps client used within the innovaphone telephony system.
