Hello there are a few things that might have happened.
AdminCP => vBGallery => Modify Settings
- Header Replacements
- Navbar Replacements
- Footer Replacements
Here you may enter a list of filenames that may appear in your header / navbar / footer that should be prefixed with your Forum's URL.
- Header: BLANK
This list is stored in the tables but also sits in the datastore cache. If that cache is empty you might fix this problem by scrolling all the way to the bottom of the setting page and hit SAVE.
If you have a custom skin / style that moved the $navbar to the top of your site in the $header you may need to copy | paste the file list of the navbar replacements to the header replacements and save again.