Redmine

While accessing the activity tab we encounter the error "Internal error
An error occurred on the page you were trying to access.
If you continue to experience problems please contact your Redmine administrator for assistance.
If you are the Redmine administrator, check your log files for details about the error."

Attaching the screenshot for more detail.
Error log is as below
"tarted GET "/projects/bihar-maintenance/activity" for 192.168.100.128 at 2016-06-24 17:15:27 +0530
Processing by ActivitiesController#index as HTML
Parameters: {"id"=>"bihar-maintenance"}
Current user: admin (id=1)
Completed 500 Internal Server Error in 78ms (ActiveRecord: 78.0ms)

NameError (uninitialized constant Meeting):
lib/redmine/activity/fetcher.rb:106:in `map'
lib/redmine/activity/fetcher.rb:106:in `constantized_providers'
lib/redmine/activity/fetcher.rb:42:in `block in event_types'
lib/redmine/activity/fetcher.rb:40:in `select'
lib/redmine/activity/fetcher.rb:40:in `event_types'
lib/redmine/activity/fetcher.rb:30:in `initialize'
app/controllers/activities_controller.rb:37:in `new'
app/controllers/activities_controller.rb:37:in `index'
lib/redmine/sudo_mode.rb:63:in `sudo_mode'"

We had configure the redmine with below configuration
Redmine 3.2.3
Ruby 2.2
mysql 5.7.2