you might need the following code:

  def respond_to?(msg_id)
    case msg_id
    when :_dump
      true
    when :marshal_dump
      false
    else
      method_missing(:respond_to?, msg_id)
    end
  end

if your file at /usr/lib/ruby/1.8/drb/drb.rb includes the line

 undef :respond_to?

and you see the following error in apaches error_log:

 [error] Wed Aug 03 15:59:39 GMT 2005 - 540596370
 TypeError
 cannot convert nil into String\n/usr/lib/ruby/1.8/drb/drb.rb:731:in `+'
 /usr/lib/ruby/site_ruby/1.8/sbsm/request.rb:73:in `join'
 /usr/lib/ruby/site_ruby/1.8/sbsm/request.rb:73:in `process'
 /home/freax/cogito/oddb.org/doc/index.rbx:10
 /usr/lib/ruby/1.8/apache/ruby-run.rb:53:in `load'
 /usr/lib/ruby/1.8/apache/ruby-run.rb:53:in `handler'