Correct errors

I create a model with relations 'childObjects' MANY_MANY .
To edit this model i add field 'childObjectsIds' and in action 'beforeSave' i modify 'childObjects'.

With standart forms it`s work, but now i get error:

if($fields===array())
throw new CDbException(Yii::t('yii','No columns are being updated for table "{table}".',

in CDbCommandBuilder on 290 line.