Check your validation rules in User model . you are try to send irrelevant data into DB. Try to change your table id as auto increment and remove the rules on your User model
its look like
public function rules()
{
return array(
array('id,username, password', 'required'), // remove id on this
array('password_repeat', 'required', 'on'=>'register'),
array('password', 'compare', 'compareAttribute'=>'password_repeat', 'on'=>'register'),
);
}
if the rules have required validator yii through validation error if you dont want validate any fields just remove fields on this list
Edited Use this for save it turn off your validation rules while save
$model->save(false);