Hi all, I am trying to run Rockstar Halo Finding with the following code. from yt.mods import * from yt.analysis_modules.halo_finding.rockstar.api import RockstarHaloFinder #find all of our simulation files files = glob.glob("RD*/*hierarchy") #hopefully the file name order is chronological files.sort() print files ts = TimeSeriesData.from_filenames(files[:]) rh = RockstarHaloFinder(ts) rh.run() but I am getting the following error. File "rockstar_halo_finding.py", line 14, in <module> rh = RockstarHaloFinder(ts) File "/home/john/yt_new/yt-x86_64/src/yt-hg/yt/analysis_modules/halo_finding/rockstar/rockstar.py", line 220, in __init__ self.pool, self.workgroup = self.runner.setup_pool() File "/home/john/yt_new/yt-x86_64/src/yt-hg/yt/analysis_modules/halo_finding/rockstar/rockstar.py", line 102, in setup_pool (self.num_writers, "writers") ] File "/home/john/yt_new/yt-x86_64/src/yt-hg/yt/utilities/parallel_tools/parallel_analysis_interface.py", line 325, in from_sizes pool.add_workgroup(size, name = name) File "/home/john/yt_new/yt-x86_64/src/yt-hg/yt/utilities/parallel_tools/parallel_analysis_interface.py", line 293, in add_workgroup group = self.comm.comm.Get_group().Incl(ranks) AttributeError: 'NoneType' object has no attribute 'Get_group' could you please explain what is going wrong here ? Thank you. -- Reju Sam John