Index: bp-core.php
===================================================================
--- bp-core.php	(revision 2770)
+++ bp-core.php	(working copy)
@@ -1460,6 +1460,9 @@
 
 	$activity = get_usermeta( $bp->loggedin_user->id, 'last_activity' );
 
+	if ( is_array( $activity ) )
+		$activity = $activity[0];
+
 	if ( !is_numeric( $activity ) )
 		$activity = strtotime( $activity );