Cannot import / referencesKeeper

Question

When starting my Authoring server, the following error is displaying and the Jahia instance is shutting down:
 

2016-10-07 21:11:16,464: ERROR [JCRSessionWrapper] - Cannot import
org.xml.sax.SAXException: /referencesKeeper
javax.jcr.PathNotFoundException: /referencesKeeper
...
Caused by: javax.jcr.PathNotFoundException: /referencesKeeper
at org.apache.jackrabbit.core.ItemManager.getItem(ItemManager.java:553)
...

Answer

No processing server was defined for this cluster.

The Authoring server was defined as the processing server and the error vanished.

However, the best practice is to always define a processing server, independent to the Authoring server, when configuring a Jahia cluster.