Okay, it seems messed up, guess the database got screwed somehow.
Try reinstalling a fresh copy of the app, will most likely be faster than troubleshooting what's wrong.
Make sure you download latest app version, from Codecanyon.
@AAJ - Not sure what you're doing there, maybe make sure you use a clean database and all as the installer itself will work just fine, so for sure there's no issue with mailwizz on this side of things.