undefined method `parse_query_parameters' for ActionController::CgiRequest:Class

I've just deployed an update to one of my sites, and now I get this error in the production log. The update was just a simple update to one of the erb templates, adding a link to the sites blog.

I've tried rolling the site back to the previous version, but the error still persists, it's all very frustrating.

The full error report is pasted below.

/!\ FAILSAFE /!\ Mon Mar 24 09:50:23 +0000 2008   Status: 500 Internal Server Error   undefined method `parse_query_parameters' for ActionController::CgiRequest:Class     /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/ cgi_process.rb:74:in `query_parameters'     /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/ request.rb:287:in `parameters'     /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/ session_management.rb:128:in `set_session_options_without_components'     /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/ components.rb:157:in `set_session_options'     /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/ session_management.rb:122:in `process'     /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/ base.rb:388:in `process'     /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/ dispatcher.rb:171:in `handle_request'     /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/ dispatcher.rb:115:in `dispatch'     /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/ dispatcher.rb:126:in `dispatch_cgi'     /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/ dispatcher.rb:9:in `dispatch'     /usr/lib/ruby/gems/1.8/gems/mongrel-1.1.3/bin/../lib/mongrel/ rails.rb:76:in `process'     /usr/lib/ruby/gems/1.8/gems/mongrel-1.1.3/bin/../lib/mongrel/ rails.rb:74:in `synchronize'     /usr/lib/ruby/gems/1.8/gems/mongrel-1.1.3/bin/../lib/mongrel/ rails.rb:74:in `process'     /usr/lib/ruby/gems/1.8/gems/mongrel-1.1.3/bin/../lib/mongrel.rb: 159:in `process_client'     /usr/lib/ruby/gems/1.8/gems/mongrel-1.1.3/bin/../lib/mongrel.rb: 158:in `each'     /usr/lib/ruby/gems/1.8/gems/mongrel-1.1.3/bin/../lib/mongrel.rb: 158:in `process_client'     /usr/lib/ruby/gems/1.8/gems/mongrel-1.1.3/bin/../lib/mongrel.rb: 285:in `run'     /usr/lib/ruby/gems/1.8/gems/mongrel-1.1.3/bin/../lib/mongrel.rb: 285:in `initialize'     /usr/lib/ruby/gems/1.8/gems/mongrel-1.1.3/bin/../lib/mongrel.rb: 285:in `new'     /usr/lib/ruby/gems/1.8/gems/mongrel-1.1.3/bin/../lib/mongrel.rb: 285:in `run'     /usr/lib/ruby/gems/1.8/gems/mongrel-1.1.3/bin/../lib/mongrel.rb: 268:in `initialize'     /usr/lib/ruby/gems/1.8/gems/mongrel-1.1.3/bin/../lib/mongrel.rb: 268:in `new'     /usr/lib/ruby/gems/1.8/gems/mongrel-1.1.3/bin/../lib/mongrel.rb: 268:in `run'     /usr/lib/ruby/gems/1.8/gems/mongrel-1.1.3/bin/../lib/mongrel/ configurator.rb:282:in `run'     /usr/lib/ruby/gems/1.8/gems/mongrel-1.1.3/bin/../lib/mongrel/ configurator.rb:281:in `each'     /usr/lib/ruby/gems/1.8/gems/mongrel-1.1.3/bin/../lib/mongrel/ configurator.rb:281:in `run'     /usr/lib/ruby/gems/1.8/gems/mongrel-1.1.3/bin/mongrel_rails:128:in `run'     /usr/lib/ruby/gems/1.8/gems/mongrel-1.1.3/bin/../lib/mongrel/ command.rb:212:in `run'     /usr/lib/ruby/gems/1.8/gems/mongrel-1.1.3/bin/mongrel_rails:281