Resolution:
Resin includes a status servlet that is useful for troubleshooting. You can enable it in resin.conf by adding it to the web-app-default element:

&ltweb-app-default>
    &ltservlet-mapping servlet-class='com.caucho.servlets.ResinStatusServlet'>
        &lturl-pattern>/resin-status</url-pattern>
        &ltinit enable="read"/>
    </servlet-mapping>
    &ltsecurity-constraint>
        &ltweb-resource-collection url-pattern="/resin-status/*"/>
        &ltip-constraint>
            &ltallow&gt127.0.0.1/32</allow>
        </ip-constraint>
    </security-constraint>

The security-constraint is there so that you can only access it from that machine, as it is not a protected servlet.

You can adjust the ip-constraint appropriately, if you do not have a browser on the same machine as the Manager.

Note that this will affect performance, and should not be done in a production environment.