If the error persists after a clean install, a Windows system file is corrupted.
Before fixing, you must understand the enemy. Call of Juarez: Gunslinger uses CEG (Custom Executable Generation), a legacy DRM system from Valve. Unlike modern Steam DRM, CEG ties the game’s executable to your specific Steam account ID. If the error persists after a clean install,
If you bought the game on GOG, you should not need Steam. However, game launchers sometimes install a Steam-emulator layer. Here is how to force the DRM-free executable. Find the original executable: Gunslinger
Gunslinger.exe.steam_api.dll or steam_apif.dll if present.Gunslinger.exe as Administrator without Steam running in the background.