Index: bp-core/bp-core-classes.php
===================================================================
--- bp-core/bp-core-classes.php	(revision 2949)
+++ bp-core/bp-core-classes.php	(working copy)
@@ -151,7 +151,7 @@
 				$sql['where_users'] = "AND u.ID IN ({$uids})";
 		}
 
-		else if ( $user_id && function_exists( 'friends_install' ) ) {
+		else if ( $user_id && bp_is_active( 'friends' ) ) {
 			$friend_ids = friends_get_friend_user_ids( $user_id );
 			$friend_ids = $wpdb->escape( implode( ',', (array)$friend_ids ) );
 
Index: bp-groups.php
===================================================================
--- bp-groups.php	(revision 2949)
+++ bp-groups.php	(working copy)
@@ -136,7 +136,7 @@
 			bp_core_new_subnav_item( array( 'name' => sprintf( __( 'Members (%s)', 'buddypress' ), number_format( $bp->groups->current_group->total_member_count ) ), 'slug' => 'members', 'parent_url' => $group_link, 'parent_slug' => $bp->groups->slug, 'screen_function' => 'groups_screen_group_members', 'position' => 60, 'user_has_access' => $bp->groups->current_group->user_has_access, 'item_css_id' => 'members'  ) );
 
 			if ( is_user_logged_in() && groups_is_user_member( $bp->loggedin_user->id, $bp->groups->current_group->id ) ) {
-				if ( function_exists('friends_install') )
+				if ( bp_is_active('friends') )
 					bp_core_new_subnav_item( array( 'name' => __( 'Send Invites', 'buddypress' ), 'slug' => 'send-invites', 'parent_url' => $group_link, 'parent_slug' => $bp->groups->slug, 'screen_function' => 'groups_screen_group_invite', 'item_css_id' => 'invite', 'position' => 70, 'user_has_access' => $bp->groups->current_group->user_has_access ) );
 			}
 		}
@@ -1110,6 +1110,13 @@
 
 	if ( !$bp->is_single_item || $bp->current_component != $bp->groups->slug || $bp->current_action != 'join' )
 		return false;
+	
+	if ( $bp->groups->current_group->status != 'public' ) {
+		if ( !groups_check_user_has_invite( $bp->loggedin_user->id, $bp->groups->current_group->id ) ) {
+			bp_core_add_message( __( 'There was an error joining the group.', 'buddypress' ), 'error' );
+			bp_core_redirect( bp_get_group_permalink( $bp->groups->current_group ) );
+		}
+	}
 
 	// user wants to join a group
 	if ( !groups_is_user_member( $bp->loggedin_user->id, $bp->groups->current_group->id ) && !groups_is_user_banned( $bp->loggedin_user->id, $bp->groups->current_group->id ) ) {