Could not connect to the CI server. Please check your settings and try again on merge request

Summary

After activating and deactivating the Jenkins CI Plugin, all project throw: Could not connect to the CI server. Please check your settings and try again On merge requests.

Steps to reproduce

Activate and Deactivate Jenkins CI Plugin.

Results of GitLab application Check

Redis version >= 2.8.0? ... yes
Ruby version >= 2.3.5 ? ... yes (2.3.6)
Git version >= 2.7.3 ? ... yes (2.14.3)
Git user has default SSH configuration? ... yes
Active users: ... 43
Elasticsearch version 5.1 - 5.5? ... skipped (elasticsearch is disabled)

Checking GitLab ... Finished

Fix:

sudo gitlab-rails console
Service.where(type: 'JenkinsService').where(active: true).each { |services|  services.active = false; services.save  };nil