Showcase theme error message

Hi,

Uploaded and installed the "Infinite SEO" plugin from my wordpress admin (did not ftp). The download and unzip seemed to work fine but when I clicked "activate" the following error message was returned (and I can no longer access any area of my wp-admin without reading the error message)...

Fatal error: Call to undefined function user_can_see_seo_metabox() in /home/depdoor/public_html/wp-content/plugins/wpmu-dev-seo-addon/wpmu-dev-seo-addon.php on line 85

This is a recent wp single site install

Thanks