A couple of the exact error messages and where you encountered the messages would be helpful, as there are a few different problems that would state 'file not found'.
If you are encountering these messages in the mod system report, then the problem is related to the mod system rather than this mod. This message is common for Mac users as the mod system fails to initialize as the game files are inside the .pck and the game cannot find the files(159) to create the backup. It can also happen for users with other OS when the folder permissions prevent the game from creating files and folders.
If you are encountering these messages though the terminal with the debug mod or the log file, then the problem is most likely failure to install the Bugfix mod before everything else, because the Bugfix mod updates the mod system in ways that are critical for adding many new folders(18) and files(174) to the game folder. If the mod folder (the one that contains "info.txt") is not named exactly "AricsExpansion", then the game will fail to find any of the custom script files in that folder, but this is only 11 files. Also, if you failed to notice file copy errors in the mod system report, then those files will likely be reported missing again at this stage.
Edit: in the event that retrying installation fails it can sometimes be useful to extract a new copies of the game and mod from the ZIP archives, or if you do not have/use the archives then re-download them. Though rare, the game folder can become corrupt after bad installs and the mod folder can become corrupt if the user accidentally moves stuff around inside. The rest of the user data folder should be safe from most problems.