Have cleaned my site as good as possible, and tried to upgrade to "com_booklibrary_pro_3.0_2014_01_27"..
At first it seems ok, but it break the site with a 500 error.
Also, in Joomla backend, it gives 500 error on both "Global Configuration", and "Media Manager"
If I uninstall BookLibrary, everything is good, But as soon as I install BookLibrary, it gives those 500 errors.