Have you tried running your epub through epubcheck? Using either Sigil or calibre's ebook editor with the epubcheck plugin installed will give you the locations of the errors. In this case, it sounds as if you are trying to use border in a place where the epub specification does not allow it to be used.
One common source is attempting to use a border with an image in an img tag.
You could use the ScrambleEbook plugin (see the
Reload this Page [GUI Plugin] ScrambleEbook: Getting help with copyrighted books thread) and then attach the scrambled version to a message in this forum.