Radiobuttonlist. Error: Object Of Class Assesstmenttmp Could Not Be Converted To String

more and more i created the ask post. i need for help.. i'm completely newbie..

hello..
i use tabular input for collecting existed data (i tried this tutorial). i have this table in mysql database

mysql> desc assesstment_tmp;
+------------+--------------+------+-----+---------+----------------+
| Field      | Type         | Null | Key | Default | Extra          |
+------------+--------------+------+-----+---------+----------------+
| id         | int(11)      | NO   | PRI | NULL    | auto_increment |
| matakuliah | varchar(255) | NO   | MUL | NULL    |                |
| silabus    | varchar(255) | YES  | MUL | NULL    |                |
| level      | tinyint(1)   | YES  |     | NULL    |                |
+------------+--------------+------+-----+---------+----------------+
4 rows in set (0.01 sec)

in index page i have

<?php echo CHtml::activeTextField($items,'[$i]matakuliah'); ?>
<?php echo CHtml::activeTextField($items,'[$i]silabus'); ?>
<?php echo CHtml::activeTextField($items,'[$i]level'); ?>

i want on last input using radio button, then i edited to

<?php echo CHtml::activeTextField($items,'[$i]matakuliah'); ?>
<?php echo CHtml::activeTextField($items,'[$i]silabus'); ?>
<?php echo CHtml::radioButtonList($items,'[$i]level',array(0=>0,1=>1,2=>2,3=>3),array(
						'labelOptions'=>array(
							'style'=>'display:inline'),'separator'=>'')) ?>

but an error i have got

Object of class AssesstmentTmp could not be converted to string

please help me..
thank you in advance..