problem saving with foreign key error

org.hibernate.exception.SQLGrammarException: could not fetch initial value for increment generator

Hi all,
i am having some issues in saving with tables with foreign key relationship. i got an error failed generate key
i got one table
ras_order
order_id number(2) primary key
order_name varchar2(100)

another table by name
ras_order_detail
order_item_id number(2) primary key,
order_item_name varchar2(100),
order_id references ras_order(order_id)

here is my basic java bean files
Order.java
public class Order {
private int order_id =0;
private String order_name = null;
private Set orderItems;

public void setOrderItemsL(Set orderitems) {
this.orderItems = orderitems;
}

public Set getOrderItemsL() {
if (this.orderItems == null) {
this.orderItems = new HashSet();
}
return this.orderItems;
}

public int getOrder_id() {
return order_id;
}

public void setOrder_id(int order_id) {
this.order_id = order_id;
}

public String getOrder_name() {
return order_name;
}

public void setOrder_name(String order_name) {
this.order_name = order_name;
}

}

OrderItem.java
public class OrderItem {
private int order_item_id = 0;
private String order_item_name = null;
private Order order = null;

public Order getOrder() {
return order;
}

public void setOrder(Order order) {
this.order = order;
}

public int getOrder_item_id() {
return order_item_id;
}

public void setOrder_item_id(int order_item_id) {
this.order_item_id = order_item_id;
}

public String getOrder_item_name() {
return order_item_name;
}

public void setOrder_item_name(String order_item_name) {
this.order_item_name = order_item_name;
}
}

here is my java code
String str = "index";
Session session = HibernateUtil.currentSession();
Transaction tx= session.beginTransaction();
Order order = new Order();
order.setOrder_name("TEST ORDER");
OrderItem oid = new OrderItem();
oid.setOrder_item_name("some name");
oid.setOrder(order);
Set oidset = new java.util.HashSet();
oidset.add(oid);
order.setOrderItemsL(oidset);
session.save(order);
tx.commit();
HibernateUtil.closeSession();
return mapping.findForward(str);

thanks
Rashid
[ December 06, 2006: Message edited by: Bear Bibeault ]

OH i forgot to add the hibernate mapping file
here it is
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">


<hibernate-mapping auto-import="true" default-lazy="false">

<class name="org.springframework.samples.petclinic.Vet" table="vets">
<id name="id" column="id">
<generator class="identity"/>
</id>
<property name="firstName" column="first_name"/>
<property name="lastName" column="last_name"/>
<set name="specialtiesInternal" table="vet_specialties">
<key column="vet_id"/>
<many-to-many column="specialty_id" class="org.springframework.samples.petclinic.Specialty"/>
</set>
</class>

<class name="org.springframework.samples.petclinic.Specialty" table="specialties">
<id name="id" column="id">
<generator class="identity"/>
</id>
<property name="name" column="name"/>
</class>

<class name="org.springframework.samples.petclinic.Owner" table="owners">
<id name="id" column="id">
<generator class="identity"/>
</id>
<property name="firstName" column="first_name"/>
<property name="lastName" column="last_name"/>
<property name="address" column="address"/>
<property name="city" column="city"/>
<property name="telephone" column="telephone"/>
<set name="petsInternal" inverse="true" cascade="all">
<key column="owner_id"/>
<one-to-many class="org.springframework.samples.petclinic.Pet"/>
</set>
</class>

<class name="org.springframework.samples.petclinic.Pet" table="pets">
<id name="id" column="id">
<generator class="identity"/>
</id>
<property name="name" column="name"/>
<property name="birthDate" column="birth_date" type="date"/>
<many-to-one name="owner" column="owner_id" class="org.springframework.samples.petclinic.Owner"/>
<many-to-one name="type" column="type_id" class="org.springframework.samples.petclinic.PetType"/>
<set name="visitsInternal" inverse="true" cascade="all">
<key column="pet_id"/>
<one-to-many class="org.springframework.samples.petclinic.Visit"/>
</set>
</class>

<class name="org.springframework.samples.petclinic.PetType" table="types">
<id name="id" column="id">
<generator class="identity"/>
</id>
<property name="name" column="name"/>
</class>

<class name="org.springframework.samples.petclinic.Visit" table="visits">
<id name="id" column="id">
<generator class="identity"/>
</id>
<property name="date" column="visit_date" type="date"/>
<property name="description" column="description"/>
<many-to-one name="pet" column="pet_id" class="org.springframework.samples.petclinic.Pet"/>
</class>

</hibernate-mapping>

MY apologies for messing it up i pasted the wrong file here is the correct file
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">


<hibernate-mapping auto-import="true" default-lazy="false">

<class name="com.model.Order" table="ras_order">
<id name="order_id" column="order_id" type="int">
<generator class="increment"/>
</id>
<property name="order_name" column="order_name"/>
<set name="orderItemsL" inverse="true" cascade="all">
<key column="order_id"/>
<one-to-many class="com.model.OrderItem"/>
</set>
</class>

<class name="com.model.OrderItem" table="ras_order_item">
<id name="order_item_id" column="order_item_id" type="int">
<generator class="increment"/>
</id>
<property name="order_item_name" column="order_item_name"/>
<many-to-one name="order" column="order_id" class="com.model.Order"/>
</class>

</hibernate-mapping>