Well, I’m testing the 4.0 Pro version on a localhost and trying to upgrade the previous 3.x Pro version of Book Library, so you FTP help proposal is not useful at all...
The problem occurs when you have category (and book) names in Cyrillic. Than the function JFilterOutput:
tringURLSafe in your router.php file produces empty strings and the books in the respective category cannot be opened.
I saw your advice in the forum to completely remove that function from router.php but this creates ugly web addresses in the browser address bar. A better solution is to replace JFilterOutput:
tringURLSafe with JFilterOutput:
tringURLUnicodeSLug
Bye the way the alias field in the category edit form does not work at all… Filtering the books with Cyrillic names using the alphabetical index is also not possible (I presume the reason is also connected to the stringURLSafe function)!
And finally, I met another difficulty when importing the books from the previous installation as you have changed the ebook download link description in the XML file.
So, to overcome the problem you have to rename
<ebookURL>...</ebookURL>
to
<ebooks><ebook><location>...</location></ebook></ebooks>
in order to preserve the locations of the previously locally uploaded ebooks.
I’ve been using the Book Library component for many years and I’m pretty happy with some of its features but I think your support and parts of the component code should be significantly improved. Wish you success in this directions!