This App uses LocalStorage to save your chosen theme, language, order of modules and background image. Unfortunately browsers do not agree on what size local storage should be. While on most browsers it is about 5000 characters (5000 KB) some browsers only allow up to about 2500 characters (2500 KB). Therefore I can't be sure what the limit for you is. You can test it yourself here.
- Reset your Background Image
- (Maybe you'll have to do your settings again)