By default the authors sidebox shows every author in the database, even if you have none of their books in the store. I have a list of authors that I could upload in the DB with a simple SQL command, to make future product creation easier, but a thousand authors without a single book would result in a less than pleasant customer experience.
So, here's a quick fix for this. The SQL query is in book_authors.php, starting at line 2.
$book_authors_query = "select distinct a.book_authors_id,
from " . TABLE_BOOK_AUTHORS . " a,
" . TABLE_BOOK_AUTHORS_INFO . " b,
" . TABLE_BOOKS_TO_AUTHORS . " c
where a.book_authors_id = b.book_authors_id AND
a.book_authors_id = c.book_authors_id
and language_id = '" . (int)$_SESSION['languages_id'] . "'
order by book_authors_name";