undefined method `find_by_sql' for Contracts:Module

I got this error when trying to run a redmine plugin on server. This plugin worked well on my local. I checked my model and db/migrate folders, everything related to Contract table are correctly. This is the full error log:

NoMethodError (undefined method `find_by_sql' for Contracts:Module):
  plugins/redmine_time_is_money/app/helpers/attendance_time_money_helper.rb:4:in `show_contract'
  plugins/redmine_time_is_money/app/controllers/attendance_time_money_controller.rb:26:in `index'
  actionpack (3.2.13) lib/action_controller/metal/implicit_render.rb:4:in `send_action'
  actionpack (3.2.13) lib/abstract_controller/base.rb:167:in `process_action'
  actionpack (3.2.13) lib/action_controller/metal/rendering.rb:10:in `process_action'
  actionpack (3.2.13) lib/abstract_controller/callbacks.rb:18:in `block in process_action'
  activesupport (3.2.13) lib/active_support/callbacks.rb:469:in `_run__2720522857436608786__process_action__2889248536667870868__callbacks'
  activesupport (3.2.13) lib/active_support/callbacks.rb:405:in `__run_callback'
  activesupport (3.2.13) lib/active_support/callbacks.rb:385:in `_run_process_action_callbacks'
  activesupport (3.2.13) lib/active_support/callbacks.rb:81:in `run_callbacks'
  actionpack (3.2.13) lib/abstract_controller/callbacks.rb:17:in `process_action'
  actionpack (3.2.13) lib/action_controller/metal/rescue.rb:29:in `process_action'
  actionpack (3.2.13) lib/action_controller/metal/instrumentation.rb:30:in `block in process_action'
  activesupport (3.2.13) lib/active_support/notifications.rb:123:in `block in instrument'
  activesupport (3.2.13) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
  activesupport (3.2.13) lib/active_support/notifications.rb:123:in `instrument'
  actionpack (3.2.13) lib/action_controller/metal/instrumentation.rb:29:in `process_action'
  actionpack (3.2.13) lib/action_controller/metal/params_wrapper.rb:207:in `process_action'
  activerecord (3.2.13) lib/active_record/railties/controller_runtime.rb:18:in `process_action'
  actionpack (3.2.13) lib/abstract_controller/base.rb:121:in `process'
  actionpack (3.2.13) lib/abstract_controller/rendering.rb:45:in `process'
  actionpack (3.2.13) lib/action_controller/metal.rb:203:in `dispatch'
  actionpack (3.2.13) lib/action_controller/metal/rack_delegation.rb:14:in `dispatch'
  actionpack (3.2.13) lib/action_controller/metal.rb:246:in `block in action'
  actionpack (3.2.13) lib/action_dispatch/routing/route_set.rb:73:in `call'
  actionpack (3.2.13) lib/action_dispatch/routing/route_set.rb:73:in `dispatch'
  actionpack (3.2.13) lib/action_dispatch/routing/route_set.rb:36:in `call'
  journey (1.0.4) lib/journey/router.rb:68:in `block in call'
  journey (1.0.4) lib/journey/router.rb:56:in `each'
  journey (1.0.4) lib/journey/router.rb:56:in `call'

So, can someone show me why method find_by_sql was undifined?