I have standard ruby-head and Rails 3.1rc4. I installed ruby-debug with following instructions from http://dirk.net/2010/04/17/ruby-debug-with-ruby-19x-and-rails-3-on-rvm/<
It looks like this is a known bug in ruby-debug-base, for the moment. I have added my comment to the issue on the bug tracker. Plase consider adding your notes as well:
http://rubyforge.org/tracker/index.php?func=detail&aid=29222&group_id=8883&atid=34290
In the meantime, ruby 1.9 has a built-in debugger; its just very slow. Manually add this require line to your code:
require 'debug'
Also, the debugger breaks on all StandardError exceptions by default, so do this when it first starts up:
catch off