Facebook update 1.2.2 – causing error on login

I’ve just updated to the newest version of the Facebook plugin (1.2.2). After uploading the new files to my site, I’m unable to login to my WordPress admin (through wp-login.php). The following message appears in the browser:

Fatal error: Call to undefined method Facebook_Loader::app_access_token_exists() in /customers/5/f/9/living-fitness.co.uk/httpd.www/blog/wp-content/plugins/facebook/admin/settings.php on line 38

Does anyone have an idea what has happened and how to resolve?

Thanks!!

Tim

http://wordpress.org/extend/plugins/facebook/