When accessing Activity-page in project I get this error:

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Internal error

An error occurred on the page you were trying to access.
If you continue to experience problems please contact your OpenProject administrator for assistance.

If you are the OpenProject administrator, check your log files for details about the error.

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The logfile reads this

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I, [2016-05-23T19:40:17.267483 #3882] INFO — : Started GET “/api/v2/projects/level_list.json” for 88.128.80.196 at 2016-05-23 19:40:17 +0200
I, [2016-05-23T19:40:17.271154 #3882] INFO — : Processing by Api::V2::ProjectsController#level_list as JSON
I, [2016-05-23T19:40:17.629480 #3882] INFO — : Rendered api/v2/projects/level_list.api.rabl (32.7ms)
I, [2016-05-23T19:40:17.630236 #3882] INFO — : Completed 200 OK in 359ms (Views: 321.9ms | ActiveRecord: 3.9ms)
I, [2016-05-23T19:40:20.279276 #3882] INFO — : Started GET “/projects/agile-test-project-01?jump=activity” for 88.128.80.196 at 2016-05-23 19:40:20 +0200
I, [2016-05-23T19:40:20.283151 #3882] INFO — : Processing by MyProjectsOverviewsController#index as HTML
I, [2016-05-23T19:40:20.283387 #3882] INFO — : Parameters: {“jump”=>“activity”, “id”=>“agile-test-project-01”}
I, [2016-05-23T19:40:20.345825 #3882] INFO — : Redirected to http://openproject.leit-werk.org/projects/agile-test-project-01/activity
I, [2016-05-23T19:40:20.399087 #3882] INFO — : Filter chain halted as :jump_to_project_menu_item rendered or redirected
I, [2016-05-23T19:40:20.399535 #3882] INFO — : Completed 302 Found in 116ms (ActiveRecord: 5.2ms)
I, [2016-05-23T19:40:20.488331 #3882] INFO — : Started GET “/projects/agile-test-project-01/activity” for 88.128.80.196 at 2016-05-23 19:40:20 +0200
I, [2016-05-23T19:40:20.492331 #3882] INFO — : Processing by ActivitiesController#index as HTML
I, [2016-05-23T19:40:20.492511 #3882] INFO — : Parameters: {“project_id”=>“agile-test-project-01”}
I, [2016-05-23T19:40:21.077748 #3882] INFO — : Completed 500 Internal Server Error in 585ms (ActiveRecord: 259.2ms)
F, [2016-05-23T19:40:21.081237 #3882] FATAL — :
ArgumentError (Missing host to link to! Please provide the :host parameter, set default_url_options[:host], or set :only_path to true):
app/models/activity/work_package_activity_provider.rb:82:in `event_url’
app/models/activity/base_activity_provider.rb:90:in `block in format_event’
app/models/activity/base_activity_provider.rb:89:in `each’
app/models/activity/base_activity_provider.rb:89:in `format_event’
lib/plugins/acts_as_activity_provider/lib/acts_as_activity_provider.rb:228:in `block in fill_events’
lib/plugins/acts_as_activity_provider/lib/acts_as_activity_provider.rb:212:in `each_with_object’
lib/plugins/acts_as_activity_provider/lib/acts_as_activity_provider.rb:212:in `fill_events’
lib/plugins/acts_as_activity_provider/lib/acts_as_activity_provider.rb:141:in `find_events_for_class’
lib/plugins/acts_as_activity_provider/lib/acts_as_activity_provider.rb:96:in `block in find_events’
lib/plugins/acts_as_activity_provider/lib/acts_as_activity_provider.rb:95:in `each’
lib/plugins/acts_as_activity_provider/lib/acts_as_activity_provider.rb:95:in `find_events’
lib/redmine/activity/fetcher.rb:98:in `block (2 levels) in events’
lib/redmine/activity/fetcher.rb:97:in `each’
lib/redmine/activity/fetcher.rb:97:in `block in events’
lib/redmine/activity/fetcher.rb:96:in `each’
lib/redmine/activity/fetcher.rb:96:in `events’
app/controllers/activities_controller.rb:53:in `index’
app/middleware/params_parser_with_exclusion.rb:40:in `call’
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