about Periodic problem

[gavinjou818]

hi friend~ i get a problem about:

Reading periodic connectivity
(18 (1 8 c d) (

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "mshconvert.py", line 1455, in convert
    scan_fluent_mesh(ifile)
  File "mshconvert.py", line 1001, in scan_fluent_mesh
    read_periodic(ifile, periodic_dx)
NameError: global name 'periodic_dx' is not defined

how can i sovle this？