Invalid workspace reference

[lottiegreenwood]

When running with two threads in mpirun and using the instrumentview results publishers, this error sometimes occurs:

Traceback (most recent call last):
  File "/usr/lib/python2.7/threading.py", line 810, in __bootstrap_inner
    self.run()
  File "/usr/lib/python2.7/threading.py", line 763, in run
    self.__target(*self.__args, **self.__kwargs)
  File "backend/instrumentview_publisher.py", line 25, in run
    self._publish()
  File "backend/instrumentview_publisher.py", line 43, in _publish
    currentws = simpleapi.CloneWorkspace(self.eventListener._rebin_for_instrumentview_transition.get_checkpoint().data)
  File "/opt/Mantid/bin/mantid/simpleapi.py", line 830, in algorithm_wrapper
    set_properties(algm, *args, **final_keywords)
  File "/opt/Mantid/bin/mantid/simpleapi.py", line 791, in set_properties
    alg_object.setPropertyValue(key, value.name())
RuntimeError: Variable invalidated, data has been deleted.