Is the PDF documet protected from changes? If so, that's your problem.
The first thing I woud do is to run a PDF syntax check in Preflight. If there is anything wrong with the document, it should report that. If there are no errors, I would try to perform the same steps with a completely different PDF document. If the same error shows up again, there is something wrong with the redaction settings, if it works, then that points again to your document. Unfortunately, there is no easy recipe to fix this problem because it could be caused by a number of different things.