Start by going through the DCERouter log (located at /var/log/pluto/DCERouter.log on the core).
If that yeilds no useful information, then open an ssh terminal and connect to the core (ssh email@example.com
then kill the DCERouter
sudo killall DCERouter
then restart the DCE Router
now watch for errors on the terminal. The bad ones will be colored, and this is much much much more verbose than the logs