Thank you for your answers! I indeed checked the documentation on WCF and executed the steps, but they did not help.
When I look in the event log, I get this error:
EventID: 8388
EventType: E
EventTime: 11/20/2014 3:39:33 PM
Source: Application_Error
EventCode: EXCEPTION
EventDescription: Message: The service '/Kentico81/CMSModules/Workflows/Services/WorkflowDesignerService.svc' cannot be activated due to an exception during compilation. The exception message is: Cannot find connection string for connection name 'AppFabricPersistenceConnectionString'.
Parameter name: connectionStringName.
Exception type: System.ServiceModel.ServiceActivationException
Stack Trace:
at System.Runtime.AsyncResult.End[TAsyncResult](IAsyncResult result)
at System.ServiceModel.Activation.HostedHttpRequestAsyncResult.End(IAsyncResult result)
at System.Web.HttpApplication.CallHandlerExecutionStep.OnAsyncHandlerCompletion(IAsyncResult ar)
Message: Cannot find connection string for connection name 'AppFabricPersistenceConnectionString'.
Parameter name: connectionStringName
Exception type: System.ArgumentException
Stack Trace:
at System.ServiceModel.Activities.Configuration.SqlWorkflowInstanceStoreElement.CreateBehavior()
at System.ServiceModel.Description.ConfigLoader.LoadBehaviors[T](ServiceModelExtensionCollectionElement`1 behaviorElement, KeyedByTypeCollection`1 behaviors, Boolean commonBehaviors)
at System.ServiceModel.Description.ConfigLoader.LoadServiceDescription(ServiceHostBase host, ServiceDescription description, ServiceElement serviceElement, Action`1 addBaseAddress, Boolean skipHost)
at System.ServiceModel.ServiceHostBase.LoadConfigurationSectionInternal(ConfigLoader configLoader, ServiceDescription description, ServiceElement serviceSection)
at System.ServiceModel.ServiceHost.ApplyConfiguration()
at System.ServiceModel.ServiceHostBase.InitializeDescription(UriSchemeKeyedCollection baseAddresses)
at System.ServiceModel.ServiceHost..ctor(Type serviceType, Uri[] baseAddresses)
at System.ServiceModel.Activation.ServiceHostFactory.CreateServiceHost(Type serviceType, Uri[] baseAddresses)
at System.ServiceModel.Activation.ServiceHostFactory.CreateServiceHost(String constructorString, Uri[] baseAddresses)
at System.ServiceModel.ServiceHostingEnvironment.HostingManager.CreateService(String normalizedVirtualPath, EventTraceActivity eventTraceActivity)
at System.ServiceModel.ServiceHostingEnvironment.HostingManager.ActivateService(ServiceActivationInfo serviceActivationInfo, EventTraceActivity eventTraceActivity)
at System.ServiceModel.ServiceHostingEnvironment.HostingManager.EnsureServiceAvailable(String normalizedVirtualPath, EventTraceActivity eventTraceActivity)
EventUrl: /Kentico81/CMSModules/Workflows/Services/WorkflowDesignerService.svc/js
EventUserAgent: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; rv:11.0) like Gecko
EventUrlReferrer: http://localhost/Kentico81/CMSModules/Workflows/Workflow_Designer.aspx?workflowid=220&objectid=220