Hiki Error

invalid byte sequence in UTF-8 (ArgumentError)
/home/nishitani/public_html/lib/hiki/util.rb:198:in `split'
/home/nishitani/public_html/lib/hiki/util.rb:198:in `unified_diff'
/home/nishitani/public_html/lib/hiki/command.rb:377:in `rescue in cmd_diff'
/home/nishitani/public_html/lib/hiki/command.rb:372:in `cmd_diff'
/home/nishitani/public_html/lib/hiki/command.rb:131:in `block in dispatch'
/usr/share/ruby/timeout.rb:66:in `timeout'
/home/nishitani/public_html/lib/hiki/command.rb:104:in `dispatch'
hiki.cgi:38:in `block in <main>'
/home/nishitani/public_html/lib/hiki/storage/base.rb:13:in `open_db'
hiki.cgi:36:in `<main>'