chart6.php missing $options array before $db_data = CGraph::get($options) is set around line 52,
I borrowed $options array from graphs.php seemed to fix it

diff chart6.php chart6.php-ORIG
52d51
< $options = array('graphids'=>$_REQUEST['graphid'], 'extendoutput'=>1, 'editable'=>1, 'nopermissions'=>1);