access denied to site coz of fatal error after activatign plugin

Hi,
I just activated the plugin but it has prevented me from accessing the website. There’s no Login link. I get this fatal error message.
Any idea how to fix this? thanks

Fatal error: Call to a member function get_page_permastruct() on a non-object in /home/emekay/AmericainArabic.net/wp-includes/link-template.php on line 271

http://wordpress.org/plugins/maintenance-mode/

http://wordpress.org/plugins/wp-maintenance-mode/