If you're using the twitter rubygem, the problem is detailed here http://groups.google.com/group/ruby-twitter-gem/browse_thread/thread/6e935089d55a92c2.
Basically the twitter gem isn't using the newest oauth gem properly, and using an older version of the oauth gem seems to fix everything. Hopefully John, the author of the twitter gem, can confirm and get a new version out soon.
