i get this exception: Illegal attempt to associate a collection with two open session


i want to delete a parent with its children. to delete a child only works great.
i have try to search but cant find anything that works for me. this is my mapping.

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly=".Core" namespace="Core">
<class name="Core.Domain.TakeAwayCategory" table="TakeAwayCategoryTbl">
<id name="Id" column="id" unsaved-value="0">
<generator class="native"></generator>
</id>
<property name="Name" column="name" />
<bag name="TakeAwayDishes" generic="true" cascade="all" inverse="true">
<key column="category_id" />
<one-to-many class="Core.Domain.TakeAwayDish" />
</bag>
</class>
</hibernate-mapping>

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="Core" namespace="Core">
<class name="Core.Domain.TakeAwayDish" table="TakeAwayDishTbl">
<id name="Id" column="id" unsaved-value="0">
<generator class="native"></generator>
</id>
<property name="Description" column="descr" />
<property name="Price" column="price" />
<property name="View" column="show" />
<property name="SortOrder" column="sortorder" />
<property name="KeyHole" column="keyhole" />
<many-to-one name="TakeAwayCategory" column="category_id" class="Core.Domain.TakeAwayCategory" />
</class>
</hibernate-mapping>

nevermind i solved it.. i did the misstake that i on the delete i send in the category object so before delete i did GetById(id); so there is my second session..