Use the "Check Cat" option on the admin screen and see if it returns anything unusual.
If that doesn't report any problems, put your category.def and categories.db files online as text files and provide the URL where we can check them out. Maybe links.cfg as well.
If that doesn't report any problems, put your category.def and categories.db files online as text files and provide the URL where we can check them out. Maybe links.cfg as well.