telecotech on "Fatar error mysql table"

hi,

i have some trouble with my php, it give me php error message like this "Fatal error: Call to a member function get_results() on a non-object..."
and my code, to print data from my table

global $wpdb;
$result = $wpdb->get_results( "SELECT * FROM MyTable ");
foreach($result as $row)
{
echo $row->name." ".$row->id."";
}
?>

any one can solve it, thanks