Insecure: can't intern tainted string (SecurityError)

/usr/local/lib/ruby/1.8/rss/parser.rb:344:in `respond_to?'
./tdiary.rb:75:in `join'
./tdiary.rb:75:in `safe'
./tdiary.rb:657:in `eval_src_orig'
(plugin/keyword_highlight.rb):24:in `eval_src'
./tdiary.rb:904:in `do_eval_rhtml'
./tdiary.rb:854:in `eval_rhtml'
index.rb:73