can't activate bp Calendar - fatal error

Hello,
I used the built in wordpress uploader/and activate to install the bp group calendar. When I hit activate it said something about an invalid header. I went back to my plugin pages and tried to activate from there and got this message-

Fatal error: Class 'BP_Group_Extension' not found in /home/soundhea/public_html/wp-content/plugins/bp-group-calendar/groupcalendar/bp-group-calendar.php on line 102

Any thoughts? Thanks!