If you encounter this issue after ftp connections working fine, you need to add following code into ​wp-config.php

[code lang=text]

if(is_admin()) { add_filter('filesystem_method', create_function('$a', 'return "direct";' )); define( 'FS_CHMOD_DIR', 0751 ); }

[/code]

Give appropriate permission to apache24 root folders and its subfolders by executing chown -R www:www /usr/local/www/apache24/data

reference: http://www.vps2.me/update-wordpress-unable-to-locate-wordpress-root-directory-installation-failed/