It looks like the exception_notification plugin is undergoing a pretty big overhaul to get it working well with rails3. The official git repository for that plugin only has one branch, master. What should you do for your existing rails2 applications that are not ready for migration to rails3?
If you are getting something somewhat like this:
rake aborted! uninitialized constant ApplicationController::ExceptionNotifiable .../rails/activesupport/lib/active_support/dependencies.rb:102:in `const_missing'
You can fix it by using commit e8b603e523c14f145da7b3a1729f5cc06eba2dd1 of that plugin.
Something like this should do the trick:
cd vendor/plugins/exception_notification git checkout -b rails2 e8b603e523c14f145da7b3a1729f5cc06eba2dd1
That particular commit is from November 13, 2008. It is the last commit not having anything to do with rails3, and it is a very stable commit and unlikely to need modification for existing projects.
if you are using externals to manage your subprojects, you can quickly fix it like this (from the main project directory):
ext freeze exception_notification e8b603e523c14f145da7b3a1729f5cc06eba2dd1