Debugger stopped working

script/server --debug and script/server --debugger lead to an error.
Despite just uninstalling and reinstalling rails and ruby-debug. It
worked 3 days ago.

:~/Workspace/my_app$ sudo gem1.8 install rails

Successfully installed rails-2.3.5
1 gem installed
Installing ri documentation for rails-2.3.5...
Installing RDoc documentation for rails-2.3.5...

:~/Workspace/my_app$ sudo gem1.8 install ruby-debug

Successfully installed ruby-debug-0.10.3
1 gem installed
Installing ri documentation for ruby-debug-0.10.3...
Installing RDoc documentation for ruby-debug-0.10.3...

:~/Workspace/my_app$ script/server --debug

=> Booting WEBrick
=> Rails 2.3.5 application starting on http://0.0.0.0:3000
You need to install ruby-debug to run the server in debugging mode.
With gems, use 'gem install ruby-debug'

Any suggestions?

Thanks,
Andrew