You use $form->dropDownListRow
that's why you will get $_POST['MyModelName']['superunit']
on your server side
Change you code like
$data=Unit::model()->findAll('sid=:sid',
array(':sid'=>(int) $_POST['MyModelName']['superunit']));
Where MyModelName
is a model that you use)
Or like
echo CHtml::dropDownList('superunit'.....
For others - this wiki may help.