500 Internal Server Error

Plugin error in '50sp.rb'.
Plugin error in '/home/htdocs/peach/diary/misc/plugin/recent_rss.rb'.
uninitialized constant RSS::VERSION
(plugin/50sp.rb):132:in `rescue in block (3 levels) in load_plugin' (TDiary::PluginError)

/home/htdocs/peach/diary/tdiary/plugin.rb:65:in `rescue in initialize'
/home/htdocs/peach/diary/tdiary/plugin.rb:56:in `initialize'
/home/htdocs/peach/diary/tdiary.rb:225:in `new'
/home/htdocs/peach/diary/tdiary.rb:225:in `load_plugins'
/home/htdocs/peach/diary/tdiary.rb:260:in `all_filters'
/home/htdocs/peach/diary/tdiary.rb:272:in `referer_filter'
/home/htdocs/peach/diary/tdiary.rb:684:in `initialize'
/home/htdocs/peach/diary/tdiary.rb:948:in `initialize'
/home/htdocs/peach/diary/tdiary/dispatcher/index_main.rb:108:in `new'
/home/htdocs/peach/diary/tdiary/dispatcher/index_main.rb:108:in `create_tdiary'
/home/htdocs/peach/diary/tdiary/dispatcher/index_main.rb:21:in `run'
/home/htdocs/peach/diary/tdiary/dispatcher/index_main.rb:6:in `run'
/home/htdocs/peach/diary/tdiary/dispatcher.rb:21:in `dispatch_cgi'
/home/htdocs/peach/diary/index.rb:36:in `<main>'