Use the command "mongrel_rails start -d " to start the ROR project, but get some error

Question

I started to learn Ruby yesterday. I used the command mongrel_rails start -d to start my Ruby on Rails project but it failed:

> F:\PlayRuby\hello>mongrel_rails start -d
C:/Ruby193/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in `require':
126: not found path   - C:/Ruby193/lib/ruby/gems/1.9.1/gems/mongrel-1.1.5-x8
6-mingw32/lib/http11.so (LoadError)
        from C:/Ruby193/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
        from C:/Ruby193/lib/ruby/gems/1.9.1/gems/mongrel-1.1.5-x86-mingw32/lib/mongrel.rb:12:in `<top (required)>'
        from C:/Ruby193/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
        from C:/Ruby193/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
        from C:/Ruby193/lib/ruby/gems/1.9.1/gems/mongrel-1.1.5-x86-mingw32/bin/mongrel_rails:11:in `<top (required)>'
        from C:/Ruby193/bin/mongrel_rails:23:in `load'
        from C:/Ruby193/bin/mongrel_rails:23:in `<main>'

I googled it, but I did not find an answer.