I tried damien_obrist solution of "Manually recreating
/apps/cq/core/content/nav/tools in CRXDE with the correct node type,
i.e. nt:unstructured and copying back the original child nodes to the
newly created "tools" node", but it dint work for me. I was still
getting the same ConstraintViolationException. As a workaround, I
created a fresh AEM instance (new AEM instance did not have
/apps/cq/core/content/nav structure) and installed the
cq-dialog-conversion-content-1.0.0.zip package successfully...