Switch from DirSync to AADSync: "An item with the same key has already been added"

Hi all,

I tried to migrate from DirSync to AADSync.

Followed the steps in http://msdn.microsoft.com/en-us/library/azure/dn783462.aspx "Install AADSync on the same server" and http://msdn.microsoft.com/en-us/library/azure/dn757602.aspx.

On step "Connect to Active Directory Domain Services" I added our forest and clicked next.

Error message appears on the bottom of the assistant: "An item with the same key has already been added."

EventViewer gives this:

System.Management.Automation.CmdletInvocationException: An item with the same key has already been added. ---> Microsoft.IdentityManagement.PowerShell.ObjectModel.SynchronizationConfigurationValidationException: An item with the same key has already been added.
   at Microsoft.DirectoryServices.MetadirectoryServices.UI.WebServices.MMSWebService.GetSchemaFromDirectory(Connector connector, Boolean commit)
   at Microsoft.IdentityManagement.PowerShell.Cmdlet.UpdateADSyncConnectorSchemaCmdlet.ProcessRecord()
   --- End of inner exception stack trace ---
   at System.Management.Automation.Runspaces.PipelineBase.Invoke(IEnumerable input)
   at Microsoft.Azure.ActiveDirectory.Synchronization.PowerShellConfigAdapter.PowerShellAdapter.TypeDependencies.InvokePipeline(Pipeline pipeline)
   at Microsoft.Azure.ActiveDirectory.Synchronization.PowerShellConfigAdapter.PowerShellAdapter.InvokePowerShellCommand(String commandName, IDictionary`2 commandParameters, Boolean isScript)
   at Microsoft.Azure.ActiveDirectory.Synchronization.PowerShellConfigAdapter.ConnectorConfigAdapter.UpdateConnectorSchema(Connector connector)
   at Microsoft.Azure.ActiveDirectory.Synchronization.Config.ConnectorAdapterBase.UpdateConnectorSchema()
   at Microsoft.Azure.ActiveDirectory.Synchronization.UserInterface.UI.WizardPages.ADDSSourceDirectoryPageViewModel.SetupADDSConnectorCore(BackgroundWorker backgroundWorker)
   at Microsoft.Azure.ActiveDirectory.Synchronization.UserInterface.UI.Controls.Wizards.ProgressReportingTaskViewModel.ExecuteAction(Action action, Boolean isProgressIndeterminate)

AADSync version I used for installation is 1.0.0475.1202.

Is there anyone who can point me in the right direction?
Would be great.

Kind regards

Sascha