display error instead of load my chart

hello.
i write one function for display data on one chart:

function charts_graphs_test2($name_lesson,$traz_lesson)
{
$canvas = chart_graphs_get_graph('open-flash');
$canvas->title = "chart_traz";
$canvas->type = "bar"; //"bar_3d";
$canvas->y_legend = "traz";
$canvas->colour = 'white';
$canvas->width = 300;
$canvas->height = 300;
$canvas->bg_colour = 'white';
foreach($traz_lesson as $key=>$element)
{
$b1[]=(int)$element;

}
$canvas->series = array(
'traz' =>$b1,
//'Page Views' => array(63,70,94,50,7,62,93,71,3),
);
// drupal_set_message(print_r($b, true));
// drupal_set_message(print_r($a, true));
$canvas->x_labels = $name_lesson;
$out = $canvas->get_chart();
return $out;
}
i have under error when my chart load:

Open Flash Chart
JSON Parse Error [Syntax Error]
Error at character 0, line 1:
0:

please help me for solve it.....