長時間ほんとすいませんorz
>>430のjson.rbをいれてみたら新しいエラーが・・・・。
いれたのはjson-1.1.7のlib配下、json.rbとjsonフォルダです。

Status: 500 Internal Error Content-Type: text/html X-CGI-Exception: 0.3.0
./json/pure.rb:13: uninitialized constant JSON::Iconv (NameError)
from ./rubygems/custom_require.rb:31:in `gem_original_require'
from ./rubygems/custom_require.rb:31:in `require'
from ./json.rb:8
from ./rubygems/custom_require.rb:31:in `gem_original_require'
from ./rubygems/custom_require.rb:31:in `require'
from ./twitter.rb:23
from insert.cgi:11:in `require'
from insert.cgi:11