Make sure you're not using the "14nightswithyou-free" or "14nightswithyou-paid" folder. If you are, you need to locate and replace it with the "14 Nights With You" folder instead.
It's best to download the latest version of 14 Days With You and the DLC. Installing them again won't lose your progress, but if you use your old save files, you likely won't be able to experience everything the DLC has to offer since it requires a brand new playthrough.