Originally Posted by Bookripper
So my question is: why do I have thousands of errors, when everything looks and works fine?
And why does my edited book look perfect when I get so much errors?
Because there's invalid xhtml present. Browsers and other readers may be more tolerant of invalid code. But invalid code is still invalid... no matter how it might render.
Element tags have to be lower-case: <a> not <A>. If it's for your own personal use and you're happy with the way it works, then don't worry about the errors. If you want to distribute the book to others and wish to have the best possible chance of it working correctly on a wide variety of devices/apps... then look into fixing the errors.