Python Exception Occurred

Traceback (most recent call last):
  File "/home/viewcvs-website/lib/viewcvs.py", line 2636, in run_cgi
    main()
  File "/home/viewcvs-website/lib/viewcvs.py", line 2611, in main
    view_log(request)
  File "/home/viewcvs-website/lib/viewcvs.py", line 1708, in view_log
    show_revs, rev_map, rev_order, taginfo, rev2tag, \
  File "/home/viewcvs-website/lib/viewcvs.py", line 1468, in read_log
    idx = string.rfind(head, '.')
  File "/usr/lib/python2.4/string.py", line 374, in rfind
    return s.rfind(*args)
AttributeError: 'NoneType' object has no attribute 'rfind'