As this happens in ParentingPostProcessor, I guess you have a cycle in your mapping hierarchy. Perhaps something like this:
<url-mapping id="my-id" parentId="my-id">
...
</url-mapping>
Make sure that there are no cycles in the hierarchy which will probably fix this issue.
See this section of the documentation for details:
http://ocpsoft.org/docs/prettyfaces/3.3.3/en-US/html/Configuration.html#config.mapping.parents