Hibernate级联高手帮帮忙啊，感激不尽！

org.springframework.orm.hibernate3.HibernateSystemException: Don't change the reference to a collection with cascade="all-delete-orphan": com.chinasofti.emotion.hrm.entity.Employee.documents; nested exception is org.hibernate.HibernateException: Don't change the reference to a collection with cascade="all-delete-orphan": com.chinasofti.emotion.hrm.entity.Employee.documents

我在employee里有设置一个set
 <set name="documents" inverse="true" cascade="all-delete-orphan" >
  <key>
  <column name="EMPLOYEEID" scale="0" not-null="true" />
  </key>
  <one-to-many class="com.chinasofti.emotion.hrm.entity.Document" />
  </set>
然后我添加employee时,第一次添加没事, 再添加时就抛出以上错误, 而且都不能再添加, 要服务器重启后才能再添加一个, 就是服务器启动一次只能加一个employee,大家帮忙看看怎么解决?? 加那个cascade="all-delete-orphan" 是为了级联删除 把employee删了的时候也能同时删了document 

谁来帮我看看啊啊。。