[ PLUGIN PROBLEM ] PLEASE HELP ME :'(

I have my site which is

http://www.seomanagementconsulting.com

and now i cannot use the admin page anymore…

I mean… im stuck… i cant use other buttons and i cant go anywhere in the page except for the page i was stuck… it all started when ive installed a plugin… and i cant even go to the plugin page to deactivate it…

this is the error message :

Fatal error: Call to undefined function is_site_admin() in /home1/golftric/public_html/seomanagementconsulting/wp-content/plugins/cd-buddybar-logo-changer/cd-bblc.php on line 36

Please2x someone help me :'(