Github user m-hogue commented on the issue: https://github.com/apache/nifi/pull/1986 @trkurc : It'd occur when the processor {{@OnScheduled}} method is called, which would prevent the processor from starting. This would be evident in the UI as a red flag on the processor when you start it: ![image](https://user-images.githubusercontent.com/7054178/28215374-cdd5ef54-687b-11e7-8698-6f45f54e33d5.png)
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