If this is the case, you will need to update your game, or if you are using a newer version that WeMod does not yet support, you will need to wait for the trainer to be updated. If the game is not listed as compatible, you might be using an unsupported version of the game. Most games have anti-modification software built into multiplayer that stops WeMod from injecting into the process.
This error may appear for a few reasons: you are attempting to use it in multiplayer or an unsupported game mode, you are running an unsupported version of the game (newer or older), your game is from an unsupported DRM, an antivirus is stopping WeMod from injecting, or we were unable to find the running process.