Updated the 3.3.1 on another site and had a similar problem on the PHP error.
PHP Fatal error: Class ‘WPSEO_Metabox_Editor’ not found in C:\inetpub\vhosts\sanclementedonor.redfontmarketing.com\httpdocs\wp-content\plugins\wordpress-seo\admin\metabox\class-metabox.php on line 42
There is another class file called class-metabox-editor.php in the same folder so i’m not sure what’s wrong. I restarted the site and the error no longer appears. Very strange bug…not sure why the call to that file would fail until the site was restarted.