Some more info (from nginx-error.log). Every other page on the site is loading fine, just the main directory page and any of the listings:
2015/02/17 16:45:56 [error] 1975#0: *1705 FastCGI sent in stderr: “PHP message: PHP Fatal error: Call to a member function get_content_title() on a non-object in /var/www/wp-content/plugins/business-directory-plugin/business-directory-plugin.php on line 1204” while reading response header from upstream, client: 173.245.56.146, server: dundalk.ie, request: “GET /members/8708/james-quinn HTTP/1.1”, upstream: “fastcgi://unix:/var/run/php5-fpm.sock:”, host: “www.dundalk.ie”
2015/02/17 16:51:25 [error] 1974#0: *1754 FastCGI sent in stderr: “PHP message: PHP Fatal error: Call to a member function metadesc() on a non-object in /var/www/wp-content/plugins/business-directory-plugin/business-directory-plugin.php on line 1269” while reading response header from upstream, client: 173.245.53.82, server: dundalk.ie, request: “GET /members HTTP/1.1”, upstream: “fastcgi://unix:/var/run/php5-fpm.sock:”, host: “www.dundalk.ie”, referrer: “https://www.dundalk.ie/”
2015/02/17 16:52:48 [error] 1974#0: *1825 FastCGI sent in stderr: “PHP message: PHP Fatal error: Call to a member function get_content_title() on a non-object in /var/www/wp-content/plugins/business-directory-plugin/business-directory-plugin.php on line 1204” while reading response header from upstream, client: 173.245.54.142, server: dundalk.ie, request: “GET /members/8689/malone-co-chartered-accountants HTTP/1.1”, upstream: “fastcgi://unix:/var/run/php5-fpm.sock:”, host: “www.dundalk.ie”