I've faced a problem using DB2
I have two tables: ParentTable and ChildTable
----ParentTable-----------------------------------------
<id name="Id" column="ID" type="Int32">
<generator class="native">
</generator>
</id>
<property name="Name" column="&quot;Name&quot;" type="String" length="255" />

<set name="Children" cascade="delete-orphan" lazy="false" inverse="true">
<key column="&quot;Parent_Id&quot;"/>
<one-to-many class="DataLayer.User, DataLayer"/>
</set>


----ChildTable-----------------------------------------
<id name="Id" column="ID" type="Int32">
<generator class="native">
</generator>
</id>
<property name="Name" column="&quot;Name&quot;" type="String" length="255" />
<many-to-one name="Parent" class="DataLayer.Parent, DataLayer" column="&quot;Parent_Id&quot;" />

When the "Child" table is empty everything is ok
otherwise I get an exception
[NHibernate.ADOException] {NHibernate.ADOException} NHibernate.ADOException
"could not initialize collection: [DataLayer.Parent.Children#1]"

Does anybody knows whats wrong