Your browser keeps a copy of all the pages and graphics it loads. It uses that to determine which site you've visited before. Sometimes people will empty it to make room on their computer or to speed things up. If you do that then your browser won't remember which page it has visited. I had forgotten that one of the peculiarities of this script is that many browsers occassionally won't recognize the link as being visited before. I'm not sure why it does it, and I'm not sure if it can be fixed.