I used the Epub metadata setting, because I liked the idea of getting the latest metadata displayed instead of the one in the file itself.
* Update Epub metadata before download
* 1 : Yes (enable)
* 0 : No
$config['cops_update_epub-metadata'] = "1";
After a while i noticed that i got a lot of errors trying to download a book. I use Wamp and cops 0.2.3 (latest version). It took me a while to discover that it was this setting that created the error. I set it back to zero and the errors stopped.
For the download i use Marvin / Stanza or Shubook on the ipad. They all gave an error when downloading the book.
Hopefully you can figure out what causes this error.