ISSUE
User Profile Synchronization service in SharePoint Stuck Starting.
When reviewing the eventlog you notice the following error every 5 seconds
ERROR
Event ID 3, Source ForeFront Identity Manager, .Net SqlClient Data Provider: System.Data.SqlClient.SqlException: HostId is not registered at
Microsoft.ResourceManagement.Data.Exception.DataAccessExceptionManager.ThrowException(SqlException innerException) at Microsoft.ResourceManagement.Data.DataAccess.RetrieveWorkflowDataForHostActivator(Int16 hostId, Int16 pingIntervalSecs, Int32 activeHostedWorkflowDefinitionsSequenceNumber, Int16 workflowControlMessagesMaxPerMinute, Int16 requestRecoveryMaxPerMinute, Int16 requestCleanupMaxPerMinute, Boolean runRequestRecoveryScan, Boolean& doPolicyApplicationDispatch, ReadOnlyCollection`1& activeHostedWorkflowDefinitions, ReadOnlyCollection`1& workflowControlMessages, List`1& requestsToRedispatch) at Microsoft.ResourceManagement.Workflow.Hosting.HostActivator.RetrieveWorkflowDataForHostActivator() at Microsoft.ResourceManagement.Workflow.Hosting.HostActivator.ActivateHosts(Object source, ElapsedEventArgs e)
RESOLUTION
The easiest way to resolve this issue is to apply the latest update to SharePoint 2010, for the latest update please see: http://technet.microsoft.com/en-us/sharepoint/ff800847.aspx
If this doesn’t work please see: http://chrishattonnzlsp.wordpress.com/2010/11/30/hostid-is-not-registered-forefront-identity-manager/
In my case, the problem was: The account I logged-in to configure User Profile Sync was not a Farm Administrator account!
I followed the troubleshooting guide, which lists all possible causes and solutions at: http://www.sharepointdiary.com/2012/09/user-profile-synchronization-service-stuck-at-starting.html#ixzz2aX7Wz4GQ