Steam Tsw6 Crashing To Desktop Since The July 14 Windows Update — Identical Ucrtbase.dll Fault Every Time

Since a Windows 11 update on July 14 replaced the system C runtime (ucrtbase.dll), TSW6 has been crashing to desktop with the exact same fault signature every time — same module, same exception code, same fault offset. Four crashes in two days on my machine, zero in the 20 days of heavy play before it. If you've had unexplained CTDs since mid-July, please check your Event Viewer (instructions below) and post whether you see the same signature — that's what will make this actionable for DTG.

The fault, from Windows Event Viewer (Application log), identical all four times:
Faulting application name: TrainSimWorld.exe, version: 4.26.1.0
Faulting module name: ucrtbase.dll, version: 10.0.26100.8875
Exception code: 0xc0000409
Fault offset: 0x00000000000a527e
Faulting module path: C:\WINDOWS\System32\ucrtbase.dll​

Why I'm pointing at the Windows update: Windows update KB5120102 replaced ucrtbase.dll — the C runtime library the game links against — on July 14 at 16:24 on my machine. The first crash of this kind ever recorded on this PC came about ten hours later. TSW6 is an Unreal Engine 4.26 title, i.e. an older binary now running against a newly tightened runtime; exception 0xc0000409 is a "fail-fast" — the runtime deliberately terminating the process when a safety check trips. The same offset every single time means it's tripping in the same place, which is exactly the kind of thing DTG can chase from a crash dump.

To check if you're affected (takes one minute):
1. Press Win+R, type eventvwr.msc, Enter.
2. Windows Logs → Application.
3. Look for red "Error" entries with source Application Error around the time of a crash.
4. If it names TrainSimWorld.exe + ucrtbase.dll + exception 0xc0000409, you're seeing the same thing — please reply with your fault offset and ucrtbase.dll version.

Full disclosure: my install runs UE4SS with a Lua mod (an overlay data reader). One of the four crashes happened with all of the mod's optional activity disabled, and the signature predates nothing else changing on the system.

I'm not suggesting anyone uninstall the Windows update — it's a security update; the fix belongs on the app side.

 

I am on windows 11 pro UpToDate with patches
and the game runs fine
or it is because you are using the ue4ss mod and the modders of that need to update it
(i do not use it)
or maybe installing this will help Latest Visual C++ Redistributable Runtimes All-in-One Jun 2026 Download | TechPowerUp