Traceback (most recent call last):
File "run_openmm.py", line 139, in <module>
simulation.context.setPositions(pdb.positions)
File "/mnt/bwpy/single/usr/lib/python3.5/site-packages/simtk/openmm/openmm.py", line 13629, in setPositions
return _openmm.Context_setPositions(self, positions)
Exception: Called setPositions() on a Context with the wrong number of positions
usually doesn't happen, why?