Sounds like file corruption. First, uninstall the mod and see if the game runs without it. If it does, redownload the mod & install it anew. Pls let me know if that helps!
EDIT: Now that I read your post again it seems like you didn't get as far as I was assuming. When exactly does that error message come up? If your browser is giving you that message and restarting your device doesn't help, try downloading with a different browser. But if the game itself is giving you that message, try the steps I described above.