Oftentimes the FlowConnector will fail when attempting to plan a Flow. If the exception message given by PlannerException is vague, use the method PlannerException.writeDOT() to export a text representation of the internal pipe assembly. DOT files can be opened by GraphViz and OmniGraffle. These plans are only partial, but you will be able to see where the Cascading planner failed.

Also note you can create a DOT file from a Flow as well via Flow.writeDOT().