ActiveRecord Association problem

Consider following class:

class Entity < ActiveRecord::Base

end

class Instance < ActiveRecord::Base

belongs_to :entity

end

Now somewhere in code, under development and test modes, this statemet

instance = Instance.find 100

1. raises exception

e = instance.entity

Raises following exception (along with stack trace):

=============================================================

NoMethodError (undefined method `entity' for #):

/vendor/rails/activerecord/lib/active_record/attribute_methods.rb:205:in `method_missing'

/vendor/rails/activerecord/lib/active_record/associations/association_proxy.rb:125:in `send'

/vendor/rails/activerecord/lib/active_record/associations/association_proxy.rb:125:in `method_missing'

/app/controllers/file_attachments_controller.rb:39:in `download'

/vendor/rails/actionpack/lib/action_controller/base.rb:1158:in `send'

/vendor/rails/actionpack/lib/action_controller/base.rb:1158:in `perform_action_without_filters'

/vendor/rails/actionpack/lib/action_controller/filters.rb:697:in `call_filters'

/vendor/rails/actionpack/lib/action_controller/filters.rb:689:in `perform_action_without_benchmark'

/vendor/rails/actionpack/lib/action_controller/benchmarking.rb:68:in `perform_action_without_rescue'

/usr/lib/ruby/1.8/benchmark.rb:293:in `measure'

/vendor/rails/actionpack/lib/action_controller/benchmarking.rb:68:in `perform_action_without_rescue'

/vendor/rails/actionpack/lib/action_controller/rescue.rb:199:in `perform_action_without_caching'

/vendor/rails/actionpack/lib/action_controller/caching.rb:678:in `perform_action'

/vendor/rails/activerecord/lib/active_record/connection_adapters/abstract/query_cache.rb:33:in `cache'

/vendor/rails/activerecord/lib/active_record/query_cache.rb:8:in `cache'

/vendor/rails/actionpack/lib/action_controller/caching.rb:677:in `perform_action'

/vendor/rails/actionpack/lib/action_controller/base.rb:524:in `send'

/vendor/rails/actionpack/lib/action_controller/base.rb:524:in `process_without_filters'

/vendor/rails/actionpack/lib/action_controller/filters.rb:685:in `process_without_session_management_support'

/vendor/rails/actionpack/lib/action_controller/session_management.rb:123:in `process'

/vendor/rails/actionpack/lib/action_controller/base.rb:388:in `process'

/vendor/rails/actionpack/lib/action_controller/dispatcher.rb:171:in `handle_request'

/vendor/rails/actionpack/lib/action_controller/dispatcher.rb:115:in `dispatch'

/vendor/rails/actionpack/lib/action_controller/dispatcher.rb:126:in `dispatch_cgi'

/vendor/rails/actionpack/lib/action_controller/dispatcher.rb:9:in `dispatch'

/vendor/rails/railties/lib/webrick_server.rb:112:in `handle_dispatch'

/vendor/rails/railties/lib/webrick_server.rb:78:in `service'

/usr/lib/ruby/1.8/webrick/httpserver.rb:104:in `service'

/usr/lib/ruby/1.8/webrick/httpserver.rb:65:in `run'

/usr/lib/ruby/1.8/webrick/server.rb:173:in `start_thread'

/usr/lib/ruby/1.8/webrick/server.rb:162:in `start'

/usr/lib/ruby/1.8/webrick/server.rb:162:in `start_thread'

/usr/lib/ruby/1.8/webrick/server.rb:95:in `start'

/usr/lib/ruby/1.8/webrick/server.rb:92:in `each'

/usr/lib/ruby/1.8/webrick/server.rb:92:in `start'

/usr/lib/ruby/1.8/webrick/server.rb:23:in `start'

/usr/lib/ruby/1.8/webrick/server.rb:82:in `start'

/vendor/rails/railties/lib/webrick_server.rb:62:in `dispatch'

/vendor/rails/railties/lib/commands/servers/webrick.rb:66

/usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:27:in `gem_original_require'

/usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:27:in `require'

/vendor/rails/activesupport/lib/active_support/dependencies.rb:496:in `require'

/vendor/rails/activesupport/lib/active_support/dependencies.rb:342:in `new_constants_in'

/vendor/rails/activesupport/lib/active_support/dependencies.rb:496:in `require'

/vendor/rails/railties/lib/commands/server.rb:39

script/server:3:in `require'

script/server:3

=============================================================

This also happens in console. We are running on Ubuntu, Postgres 8.2

We are not able to detect why this happens as its not the case everywhere.