Dear All, When i use the command genbox -ci single.gro -nmol 175 -box 7.5 7.5 7.5 -try 100 -o 175_noW.gro the error is Segmentation fault (core dumped) What does it mean ? And if i reduce the -try value, the out put file does not contain the right number of residues (not 175, and less than). Thank for any help ! Regards, KT