fix buddy press: 'BP_Group_Extension' not found

I made a change to buddypress in backend and it caused this error:

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Fatal error: Class ‘BP_Group_Extension’ not found in /home/content/01/11915301/html/members/wp-content/plugins/bp-group-calendar/groupcalendar/bp-group-calendar.php on line 103

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can see it at:

http://musclemindmotivation.com/members/

i can’t get into the backend to fix it. wont let me go to wp-admin

fyi: its a second install of wordpress on sub directory members.