I know people have reported the "Repeated column in mapping issue" earlier but I am not using the key-many-to-one element. My scenario is simple. I have a one-to-many between a department table and an employee table. I am using composite keys in employee table (dept_id, emp_id). I get the following error:

Repeated column in mapping for class model.Employee should be mapped with insert="false" update="false": dept_id

Following are the details:

Hibernate version: 2.1

Mapping documents:
<hibernate-mapping>

<class name="model.Dept" table="department">

<id name="deptId" column="dept_id" type="int" unsaved-value="0">
<generator class="assigned"/>
</id>

<property name="deptName" column="dept_name" type="string"/>


<set name="employees" outer-join="true" inverse="true" cascade="all">
<key>
<column name="dept_id"/>
</key>
<one-to-many class="model.Employee"/>
</set>

</class>

<class name="model.Employee" table="employee">

<composite-id>
<key-property name="deptId" column="dept_id" type="int"/>
<key-property name="empId" column="emp_id" type="int"/>
</composite-id>

<property name="empName" column="emp_name" type="string"/>

<many-to-one name="dept" class="model.Dept">
<column name="dept_id"/>
</many-to-one>

</class>

</hibernate-mapping>

Code between sessionFactory.openSession() and session.close():

Full stack trace of any exception that occurs:
Repeated column in mapping for class model.Employee should be mapped with insert="false" update="false": dept_id
Name and version of the database you are using: Mysql 4.1
The generated SQL (show_sql=true):

Debug level Hibernate log excerpt:

The limitations section of the reference (section 8.2) says "there is no way to map any association to multiple foreign keys". Can you please elaborate on this limitation? Does this mean that the employees collection cannot be inserted when I insert a department object? Is this the limitation I am hitting?

This is not the appropriate reference.
You cannot set the same DB value twice in your object model. So if you set deptId in your composite PK, then you must set many-to-one as insert=false unpdate=false... or use key-many-to-one