Here are some solutions:
1. If you're saying the file is in the game files, then the file must be broken. Just copy and paste a new System2c file from the installed RTP and replace it.
2. If the file in the system2 folder isn't there, copy and paste the System2c file from the RTP and put it in the system2 folder in the game.
I think you'll get a new error if you do this, it'll say that the vehicle file could not be found. Just copy a new vehicle folder from the RTP and place it in the CharSet folder in the game files.
I got this error with all of FG7's games, so I know how to handle this. Don't worry! It's common!