What error ? As process designer I want to know what problem there is behind, from tomcat console I can get:
09:57:35,917 [http-nio-8080-exec-6] WARN org.activiti.engine.impl.bpmn.parser.BpmnParse - Invalid reference in 'bpmnElement' attribute, sequenceFlow flow1 not found 09:57:35,918 [http-nio-8080-exec-6] WARN org.activiti.engine.impl.bpmn.parser.BpmnParse - Invalid reference in 'bpmnElement' attribute, sequenceFlow flow2 not found
My point is not related to a specific process definition, but add some sort of help to users to understand errors on interface level, not on console level
That is something we might add in the future, but currently it's not in yet. (Note that the commercial version does have validation like that if you are interested in that)