I recently upgraded a project from Rails 2.3.2 to 2.3.3, after which I started getting strange the following error from Passenger:

undefined method 'rewind' for #<UNIXSocket:0xf6206c18>

After a little Googling, I discovered that I also needed to upgrade passenger from 2.1.2 to the current version 2.2.4. If you're using RubyGems, this is a quick and easy:

gem update passenger
passenger-install-apache2-module

Once the Passenger installation has finished, be sure to update your apache config to point to the new version of Passenger:

# apache2.conf
LoadModule passenger_module /usr/lib/ruby/gems/1.8/gems/passenger-2.2.4/ext/apache2/mod_passenger.so
PassengerRoot /usr/lib/ruby/gems/1.8/gems/passenger-2.2.4
PassengerRuby /usr/bin/ruby1.8