Wallpaper borders are frequently installed with a special glue called "border adhesive" or "vinyl-to-vinyl adhesive". This glue is very similar to common white glue (ElmersŪ Glue) and can not be removed with wallpaper removers including DIF. There is no easy way to remove borders installed with these glues. Begin by dry scraping as much of the border off as possible using a Paper Scraper. After scraping sand off the remaining portion with 100 grit sandpaper. Expect some wall damage. You might also want to try goof off or goo-be-gone as I have heard that they have helped.