Hi again, How about this one ... Traceback (most recent call last): File "/usr/local/phenix-1.6.1-348/phenix/phenix/command_line/refine.py", line 11, in <module> command_line.run(command_name="phenix.refine", args=sys.argv[1:]) File "/usr/local/phenix-1.6.1-348/phenix/phenix/refinement/command_line.py", line 71, in run overwrite = command_line_interpreter.command_line.options.overwrite) File "/usr/local/phenix-1.6.1-348/phenix/phenix/refinement/driver.py", line 413, in __init__ self.process_ncs_restraint_groups() File "/usr/local/phenix-1.6.1-348/phenix/phenix/refinement/driver.py", line 672, in process_ncs_restraint_groups log = log) File "/usr/local/phenix-1.6.1-348/cctbx_project/mmtbx/ncs/restraints.py", line 306, in from_atom_selections log=log) File "/usr/local/phenix-1.6.1-348/cctbx_project/mmtbx/ncs/restraints.py", line 219, in __init__ assert n_ncs > 0 AssertionError Thanks again, Robert