If you’re trying to use web.config transformations in VS 2010 with nHibernate you might be hitting the same issue I’ve been getting the transformation to match the hibernate-configuration node. The reason is because you have to specify an xmlns="urn:nhibernate-configuration-2.2" attribute as part of the configuration:

<configuration>
<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
    <session-factory>
      <property name="connection.connection_string">connection string</property>
      ...
    </session-factory>
  </hibernate-configuration>
</configuration>

To fix, just set the namespace on the target node in the transformation file like this:

<configuration xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform"
               xmlns:hib="urn:nhibernate-configuration-2.2">
  <hib:hibernate-configuration>
    <hib:session-factory>
      <hib:property xdt:Transform="Replace" xdt:Locator="Match(name)" name="connection.connection_string">your connection string</hib:property>
    </hib:session-factory>
  </hib:hibernate-configuration>
</configuration>