Did you unzip the base game as well? You might be trying to put the "14 Nights With You" folder inside a zipped/archived folder — or a folder that you don't have permission to edit.
Please check which files you've installed, and make sure you didn't accidentally copy or move anything other than the unzipped "14 Nights With You" folder.
If you still get that error after verifying your files, then you may need to completely delete the base game and the DLC, re-download them again, and then reinstall everything.