org.springframework.orm.hibernate3.HibernateOptimisticLockingFailureException: Batch update returned unexpected row count from update [0]; actual row count: 0; expected: 1; nested exception is org.hibernate.StaleStateException: Batch update returned unexpected row count from update [0]; actual row count: 0; expected: 1

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="com.bean.test" table="test" dynamic-insert="true" dynamic-update="true" >
        <id name="restaurantId" type="java.lang.Long">
            <column name="restaurant_id" />
            <generator class="com.bean.commons.CustomIdGenerator" />
        </id>

import java.io.Serializable;

import org.hibernate.HibernateException;
import org.hibernate.engine.SessionImplementor;
import org.hibernate.id.IdentifierGenerator;
import org.hibernate.id.IdentifierGeneratorFactory;
import org.hibernate.persister.entity.EntityPersister;

public class CustomIdGenerator implements IdentifierGenerator
{

   @Override
   public Serializable generate(SessionImplementor sessionImplementor, Object object) throws HibernateException
   {
      try
      {
      System.out.println("in custom generator..."+object.getClass().getCanonicalName());
      EntityPersister entityPersister = sessionImplementor.getEntityPersister("restaurantId", object);
      
      Serializable id = entityPersister.getIdentifierGenerator().generate(sessionImplementor, "restaurantId");
      
      System.out.println("id is "+id);
      if(id == null)
      {
         return IdentifierGeneratorFactory.POST_INSERT_INDICATOR;
      }
      
      return id;
      }
      catch (Exception e)
      {
         System.out.println("in exception ");
         System.out.println(e.getMessage());
         return null;
      }
   }

}

extends  IdentityGenerator

public class UIGenerator extends  IdentityGenerator
{
     public Serializable generate(SessionImplementor session, Object object) throws HibernateException
   {
      //
                long id = generateMyID();
                if (id == null)
         return IdentifierGeneratorHelper.POST_INSERT_INDICATOR; //asking Hibernate to generate ID
         
        }
}