The Ultimate Solution for the "Unable to create steam appid.txt. mw3" Error on Steam
First of all, on your computer the New World Launcher.exe is not the most stable application. Therefore, if the New World Launcher crashes, the Steam Subsystem cannot launch the game and you will get the steam_appid.txt issue. So, when your game crashes try launching it using New World Launcher. Its a small and simple application, but it will get the job done. There is no need to install it. If the error still persists, you can look into other possible causes. Here are some helpful websites to help you do that. Steamworks first-time error Steam Subsystem Uninstalled
Unable to create steam appid.txt. mw3
If your game crashed when it tried loading Steamworks and the New World Launcher was not helpful, the issue may happen when trying to create the steam_appid.txt file. Although, I have no proof, some players are reporting that this error is happening while looking for an empty folder to place the steam_appid.
In this case, the NewWorldLauncher.exe failed to create the steam_appid.txt file. The problem here is the application NewWorldLauncher.exe is not designed to handle an open file. Its the launcher and not the New World Launcher. This means that you should be using NewWorldLauncher.exe, not NewWorldLauncher.exe.config. If you are still getting the error, the launcher is not able to locate the steam_appid.txt file on your computer. In order for the launcher to create the steam_appid.txt file, you need to place it in your UnrealEngine3ApplicationInstanceConfig.xml file.
<AppInstanceConfig0> <SteamAppsPath>C:\Steam\SteamApps\Common\UnrealEngine 3</SteamAppsPath> <SteamAppIdFile>steam_appid.txt</SteamAppIdFile> <SteamAppIdFilePath>C:\Steam\steamapps\common\UnrealEngine 3</SteamAppIdFilePath> </AppInstanceConfig0> Unable to create steam appid.txt. mw3 This is the file where the New World Launcher wants to create the steam_appid.txt file for you. However, the application is failing to locate that file on your computer. This is because the launcher is trying to locate the steam_appid.txt file using the UnrealEngine3AppInstanceConfig.xml configuration file, as you can see in the following picture.