SharePoint 2010, 3 farms: Collaboration, Service apps, FAST
When users hit the site, they get "Unexpected Error occurred" and a correlation ID. After reviewing the ULS log, I find the following:
User Profile Exception occured while connecting to WCF endpoint: System.ServiceModel.Security.SecurityAccessDeniedException: Access is denied.
Grant full control permission to the UPS service app for the web application app pool service account and the farm service account of the Collaboration farm:
Go to the Central Admin of the farm that is hosting the UPS service app, Central Administration > User Profile Service Application Instance > Permissions