Thanks for your responses. I finally figured out what the problem was. The culprit was due to a one-to-one mapping on a primary key association. I am not able to get this one to one association to work, even after following the text book definition of defining the primary key on the child.
Code:
<id name="CaseID" column="CaseID">
<generator class="foreign">
<param name="property">Case</param>
</generator>
</id>
Both sides of the relationship have been defined using one-to-one association with the constrained="true" set on the child side of the association.