I am running yt-2.1stable with python2.7 on Kraken and run into this problem: When I call a derived quantity that calls a derived field that calls a universal field, I get an error: "AttributeError: 'fake_parameter_file' object has no attribute 'parameters'" which arises in the universal field's convert function in 'data_objects/universal_fields.py' With the following code: #derived Field def _test2(field,data): return data['Baryon_Overdensity'] add_field('test2',function=_test2,units=r"") #derived quantity def _test(data): return data['test2'] def _combTest(data,arr): return arr.sum() add_quantity('test',function=_test,combine_function=_combTest,n_ret=1) dd.quantities['test']() I get the error: AttributeError: 'fake_parameter_file' object has no attribute 'parameters' from line 418, in _Convert_Baryon_Overdensity in universal_fields.py: "data.pf.parameters.has_key('omega_baryon_now'):" So it seems as if the parameter file is not being passed from the derived quantitty all the way to the universal field. This works fine when I run it in serial, but fails when it is ran in parallel. Any suggestions? Thanks