500 Internal Server Error

invalid byte sequence in UTF-8 (ArgumentError)

/home/yabuki/lib/ruby/2.0.0/cgi/util.rb:36:in `gsub'
/home/yabuki/lib/ruby/2.0.0/cgi/util.rb:36:in `escapeHTML'
/home/yabuki/lib/ruby/2.0.0/erb.rb:932:in `html_escape'
(erb):22:in `rescue in eval_rhtml'
/home/yabuki/lib/ruby/2.0.0/erb.rb:849:in `eval'
/home/yabuki/lib/ruby/2.0.0/erb.rb:849:in `result'
/home/yabuki/public_html/diary/tdiary/base.rb:36:in `rescue in eval_rhtml'
/home/yabuki/public_html/diary/tdiary/base.rb:29:in `eval_rhtml'
/home/yabuki/public_html/diary/tdiary/view.rb:140:in `eval_rhtml'
/home/yabuki/public_html/diary/tdiary/dispatcher/index_main.rb:43:in `run'
/home/yabuki/public_html/diary/tdiary/dispatcher/index_main.rb:6:in `run'
/home/yabuki/public_html/diary/tdiary/dispatcher.rb:26:in `dispatch_cgi'
/home/yabuki/public_html/diary/index.rb:33:in `<main>'