A required file prefix is missing.
This error indicates that a required file prefix is missing. Most often, this is associated with disk or disk assisted queues. In that context, it means that either the file base name or the directory pointed to it are not set. A common cause (at least for pre v6 versions) is that multiple ruleset queues are defined, but a queue file name is only given once. Then, the name applies only for the first queue. All other properly start up, but with auto-generated names (which is a bit dangerous, as these names depend on the order in which queues appear inside the config file). This situation should be fixed be providing file names for all queues.