Anything that prevents you from playing the game properly. Do you have issues playing for the game, downloading it or successfully running it on your computer? Let us know here.
you have played it before and there are parts of a mod. Delete them and be fine.
In windows go to the %appdata%/factorio/mods folder and delete what is there and then start a new game.
It looks like the mod isn't compatible with the current version of the game. Did you check the download post to see if it was compatible with the latest version of 0.12?
If you want to get ahold of me I'm almost always on Discord.