To fix this problem:
Open admin.vehiclemanager.php and search for this line:
$num_cylinder_list = mosHTML :: selectList($numcylinder, 'vcylinder', 'class="inputbox" size="1"', 'value', 'text', $vehicle->cylinder);
Change it to
$num_cylinder_list = mosHTML :: selectList($numcylinder, 'cylinder', 'class="inputbox" size="1"', 'value', 'text', $vehicle->cylinder);
And it works!
I hope i can help other users.