I am using Hibernate 2.1.3 with Oracle 9i

I am getting a net.sf.hibernate.MappingException: No persister for: java.lang.String

Here is the mapping file:
----------------------------

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

<hibernate-mapping>
<class name="com.amg.condenet.ad.domain.AdSuppression" table="AD_SUPPRESSION" mutable="false">
<composite-id>
<key-property name="mbid" column="mbid" type="string" />
<key-property name="placement" column="placement" type="java.lang.string" />
</composite-id>
</class>
</hibernate-mapping>

Here is the code:
-------------------
Query query =
session.createQuery("select count(*) from
com.amg.condenet.ad.domain.AdSuppression adSuppression " +
"WHERE adSuppression.mbid =? AND adSuppression.placement =?");

query.setEntity(0, mbid);
query.setEntity(1, placement);
query.setMaxResults(1);

int count = ((Integer) query.iterate().next()).intValue();

----------------------

The interesting thing is that if I change the query definition to the following and remove the query.setEntity statements, it works fine:

Query query =
session.createQuery("select count(*) from
com.amg.condenet.ad.domain.AdSuppression adSuppression " +
"WHERE adSuppression.mbid = '" + mbid + "' AND
adSuppression.placement = '" + placement + "'");


Any thoughts?

The mapping file has the line:

<key-property name="placement" column="placement" type="java.lang.string" />

That actually reads:

<key-property name="placement" column="placement" type="string" />