First of all I moved all my books and tested it with a very small library and folders tree. Same problem occurs.
I also forwarded the port on my router to test the access via hostname and fully qualified dns name. no good news too.
Here's a bit of my log, tell me how can I send the wole file to you, if needed.
I'm really appreciating your help 
Code:
[Sat Apr 12 23:32:41 2014] [notice] Graceful restart requested, doing restart
[Sat Apr 12 23:32:41 2014] [notice] Digest: generating secret for digest authentication ...
[Sat Apr 12 23:32:41 2014] [notice] Digest: done
[Sat Apr 12 23:32:42 2014] [notice] Apache/2.2.27 (FreeBSD) PHP/5.4.26 mod_ssl/2.2.27 OpenSSL/0.9.8y DAV/2 configured -- resuming normal operation
s
[Sat Apr 12 23:42:56 2014] [error] [client 2.231.176.110] File does not exist: /usr/local/www/apache22/data/cops/download, referer: http://xxx:8080/index.php?page=3&id=179
[Sat Apr 12 23:43:34 2014] [error] [client 2.231.176.110] File does not exist: /usr/local/www/apache22/data/cops/download, referer: http://xxx/index.php?page=3&id=179
[Sat Apr 12 23:45:41 2014] [error] [client 2.231.176.110] File does not exist: /usr/local/www/apache22/data/cops/cops
[Sat Apr 12 23:45:48 2014] [error] [client 2.231.176.110] File does not exist: /usr/local/www/apache22/data/cops/download
[Sat Apr 12 23:48:16 2014] [error] [client 2.231.176.110] File does not exist: /usr/local/www/apache22/data/cops/download, referer: http://xxx:8080/index.php?page=3&id=867
[Sun Apr 13 09:26:59 2014] [error] [client 192.168.1.129] File does not exist: /usr/local/www/apache22/data/cops/download, referer: http://192.168.1.103:8080/index.php?page=3&id=1