hibernate version: 2.0.3

hi, i've got the following exception when i try to save an object:

[java] net.sf.hibernate.HibernateException: Illegal attempt to associate a collection with two open sessions
[java] at net.sf.hibernate.collection.PersistentCollection.setSession(PersistentCollection.java:188)
[java] at net.sf.hibernate.impl.SessionImpl.removeCollectionsFor(SessionImpl.java:1076)
[java] at net.sf.hibernate.impl.SessionImpl.removeCollectionsFor(SessionImpl.java:1047)
[java] at net.sf.hibernate.impl.SessionImpl.doUpdate(SessionImpl.java:1291)
[java] at net.sf.hibernate.impl.SessionImpl.saveOrUpdate(SessionImpl.java:1206)
[java] at com.pcxion.genesis.product.Catalogue.save(Catalogue.java:50)
[java] at com.pcxion.genesis.test.Test.main(Test.java:45)

mapping file:
*** Catalogue.hbm.xml ***
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 2.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping>

<class name="com.pcxion.genesis.product.Catalogue" table="catalogue">

<id name="id" column="id" type="long" unsaved-value="0">
<generator class="hilo">
<param name="table">hilo_tbl</param>
<param name="column">next</param>
</generator>
</id>
<property name="name" type="string" not-null="true"/>
<property name="description" type="string" not-null="false"/>
<property name="flgDefault" type="boolean" not-null="true"/>
<set name="categories" cascade="all">
<key column="catalogue_id"/>
<!--index column="seq"/--> <!-- sequence of each tx item-->
<one-to-many class="com.pcxion.genesis.product.Category"/>
</set>
</class>

</hibernate-mapping>

*** Category.hbm.xml ***
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 2.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping>

<class name="com.pcxion.genesis.product.Category" table="category">

<id name="id" column="id" type="long" unsaved-value="0">
<generator class="hilo">
<param name="table">hilo_tbl</param>
<param name="column">next</param>
</generator>
</id>
<property name="name" type="string" not-null="true"/>
<property name="description" type="string" not-null="false"/>

<!-- many children to parent -->
<many-to-one name="parent" column="parent_id"/>

<!-- parent has many children -->
<set name="subCategories" inverse="true" cascade="all">
<key column="parent_id"/>
<one-to-many class="com.pcxion.genesis.product.Category"/>
</set>

<set name="products" table="category_product">
<key>
<column name="cat_id" not-null="true"/>
</key>
<many-to-many class="com.pcxion.genesis.product.Product">
<column name="p_id" not-null="true"/>
</many-to-many>
</set>

</class>

</hibernate-mapping>

*** Product.hbm.xml ***
...
<set name="groupings" table="category_product" inverse="true" lazy="false">
<key>
<column name="p_id" not-null="true"/>
</key>
<many-to-many class="com.pcxion.genesis.product.Category">
<column name="cat_id" not-null="true"/>
</many-to-many>
</set>
...


The code that causes the exception:
Product p = new Product();
p.setProductCode("0110");
p.setShortDesc("product test");
p.setLongDesc("long desc");
p.setCtnCost(10.00);
p.setRrp(0.00);
p.setCtnQty(1);
p.setOrderCode("xxx");
p.setGstCode(Product.GST_10);
p.setMinOrdQty(1);

Catalogue c = (new Catalogue()).findById(917505); // Report groups
Category cat = new Category();
cat.setName("category with products");
cat.setDescription("cat a description");
cat.setParent(null);
cat.addProduct(p);
p.addGrouping(cat);
c.addCategory(cat);

try{
//cat.save();
c.save(); // <---- *** exception here
p.save();
}catch(Exception e){
e.printStackTrace();
}
...

Catalogue.save() method:

...
try{
Session session = Database.getInstance().newSession();
session.saveOrUpdate(this); // <---- exception here
session.flush();
session.close();
}catch(Exception e){
e.printStackTrace();
throw new Exception(e);
}
...


I don't have two open sessions at the same time, can somebody help me please

SORRY guys, i forgot to close the session in one of my Catalogue.findXXX methods.