railsの問題というよりもgemがおかしくなった気がします。
動いているほうのマシンではgem 0.9.4 で動かなくなったほうは 1.1.1　です。

% gem uninstall mongrel
Select gem to uninstall:
 1. mongrel-1.0.1-x86-mswin32
 2. mongrel-1.1.5-x86-mswin32-60
 3. All versions
> 3
INFO:  In order to remove mongrel, please execute:
        gem uninstall mongrel --install-dir=C:/Ruby/lib/ruby/gems/1.8

% gem uninstall gettext
INFO:  In order to remove gettext, please execute:
        gem uninstall gettext --install-dir=C:/Ruby/lib/ruby/gems/1.8

% gem -v
1.1.1

% gem uninstall mongrel --install-dir=C:/Ruby/lib/ruby/gems/1.8

Select gem to uninstall:
 1. mongrel-1.0.1-x86-mswin32
 2. mongrel-1.1.5-x86-mswin32-60
 3. All versions
> 3
INFO:  In order to remove mongrel, please execute:
        gem uninstall mongrel --install-dir=C:/Ruby/lib/ruby/gems/1.8

% gem uninstall -a mongrel
INFO:  In order to remove mongrel, please execute:
        gem uninstall mongrel --install-dir=C:/Ruby/lib/ruby/gems/1.8

--
ML: rails@r...
使い方: http://QuickML.com/