I have this same issue with a tab for my PhotoPost vBGallery. The only difference from other tabs is that the target URL is in a directory under public_html instead of being in the forum directory.
There are two issues.
- The tab works correctly the first time but when you click to any link on the gallery page, the tab highlight moves back to the Forum tab.
- After selecting the Gallery tab, clicking any other tab results in a 404 error because the path into the gallery directory is concatenated into the URL.