Hi, I am trying to refine using the following twin operators output from xtriage for C2221 1/2*h-1/2*k,-3/2*h-1/2*k,-l 1/2*h+1/2*k,3/2*h-1/2*k,-l but phenix.refine (vers 1.4-4 and 1.4-3) fails with the following error message: =============================== refinement start ============================== Traceback (most recent call last): File "/usr/progs/linux/phenix-1.4-4/phenix/phenix/command_line/refine.py", line 18, in <module> command_line.run(command_name="phenix.refine", args=sys.argv[1:]) File "/usr/progs/linux/phenix-1.4-4/phenix/phenix/refinement/command_line.py", line 89, in run call_back_after_monitor_collect=call_back_after_monitor_collect) File "/usr/progs/linux/phenix-1.4-4/phenix/phenix/refinement/driver.py", line 1121, in run call_back_after_monitor_collect = call_back_after_monitor_collect) File "/usr/progs/linux/phenix-1.4-4/phenix/phenix/refinement/strategies.py", line 191, in refinement_machine twin_law = sgtbx.rt_mx( params.twinning.twin_law ) RuntimeError: cctbx InternalError: /net/anaconda/scratch1/phenix/phenix-1.4-4/cctbx_project/cctbx/sgtbx/rt_mx.cpp(230): Unsuitable value for rational rotation matrix. I am running the RedHat WS 5.2 64-bit OS. Thanks for suggestions, Alex -- Alex Taylor, Ph.D. Technical Director, X-ray Crystallography Core Laboratory University of Texas Health Science Center at San Antonio Office: 210-567-3781 FAX: 210-567-6595