Hmm...I believe I had the same issue you did. I know you don't want to (because it is 11GB) but I would advise deleting the CUP file you have and re-download it. Sometimes the download messes up and causes issues. Make sure you are downloading CUP from the link provided you, don't do it through Steam Workshop. This is about the limit of my knowledge, if this doesn't work then someone with a little more know how needs to post here lol.