I have a table named REQUIRMENTS , i gave this exception when i want to delete a record :

nested exception is org.hibernate.ObjectDeletedException: deleted object would be re-saved by cascade (remove deleted object from associations)

the hbm.xml file is :
.....
........
<many-to-one name="parent" cascade="none">
<column name="REQ_PARENT_ID" not-null="false"/>
</many-to-one>
<bag name="children" cascade="all-delete-orphan" inverse="true" lazy="true" batch-size="10">
<key column="REQ_PARENT_ID"/>
<one-to-many class="com.navaco.model.project.Requirement" not-found="ignore"/>
</bag>


<list name="preRequirements"
table="PRE_REQUIRMENTS"
cascade="all">
<key column="PRQ_REQ_REFRENCE"/>
<list-index column="PRQ_ID"/>
<composite-element
class="com.navaco.model.project.PreRequirement">
<property name="percentage" column="PRQ_PERCENTAGE" type="float"/>
<many-to-one class="com.navaco.model.project.Requirement" name="refered" column="PRQ_REQ_REFERED"/>
</composite-element>
</list>
......
........

I think i have done every thing write , dose any body know what is the problem ??