When adding or removing a share the actions on server are executed twice, which causes exceptions in log files (function is not affected).

The function calls are coming from different threads. Issue could be related to parallel running IPv4 and IPv6 UPnP servers, maybe both receiving the command.

h4. Additional Information
[2013-05-03 22:58:37,885] [213124 ] [29 ] [INFO ] - MediaLibrary: Removing share 'd0de18f5-b0e7-4f98-8300-23ee839f9474'
[2013-05-03 22:59:20,427] [255666 ] [27 ] [INFO ] - MediaLibrary: Removing share 'd0de18f5-b0e7-4f98-8300-23ee839f9474'
[2013-05-03 22:59:20,445] [255684 ] [27 ] [WARN ] - SOAPHandler: Error invoking UPnP action 'RemoveShare'
System.NullReferenceException: Der Objektverweis wurde nicht auf eine Objektinstanz festgelegt.
   bei MediaPortal.Backend.Services.MediaLibrary.MediaLibrary.TryCancelLocalImportJobs(Share share) in D:\Coding\MP\MP2\MP2_git\MediaPortal-2\MediaPortal\Source\Core\MediaPortal.Backend\Services\MediaLibrary\MediaLibrary.cs:Zeile 414.
   bei MediaPortal.Backend.Services.MediaLibrary.MediaLibrary.RemoveShare(Guid shareId) in D:\Coding\MP\MP2\MP2_git\MediaPortal-2\MediaPortal\Source\Core\MediaPortal.Backend\Services\MediaLibrary\MediaLibrary.cs:Zeile 1050.
   bei MediaPortal.Backend.Services.ClientCommunication.UPnPContentDirectoryServiceImpl.OnRemoveShare(DvAction action, IList`1 inParams, IList`1& outParams, CallContext context) in D:\Coding\MP\MP2\MP2_git\MediaPortal-2\MediaPortal\Source\Core\MediaPortal.Backend\Services\ClientCommunication\UPnPContentDirectoryServiceImpl.cs:Zeile 775.
   bei UPnP.Infrastructure.Dv.DeviceTree.DvAction.FireActionInvoked(IList`1 inParams, IList`1& outParams, CallContext context) in D:\Coding\MP\MP2\MP2_git\MediaPortal-2\MediaPortal\Source\Core\UPnP\Infrastructure\Dv\DeviceTree\DvAction.cs:Zeile 146.
   bei UPnP.Infrastructure.Dv.DeviceTree.DvAction.InvokeAction(IList`1 inParameters, IList`1& outParameters, Boolean checkSignature, CallContext context) in D:\Coding\MP\MP2\MP2_git\MediaPortal-2\MediaPortal\Source\Core\UPnP\Infrastructure\Dv\DeviceTree\DvAction.cs:Zeile 129.
   bei UPnP.Infrastructure.Dv.SOAP.SOAPHandler.HandleRequest(DvService service, Stream messageStream, Encoding streamEncoding, Boolean subscriberSupportsUPnP11, CallContext context, String& result) in D:\Coding\MP\MP2\MP2_git\MediaPortal-2\MediaPortal\Source\Core\UPnP\Infrastructure\Dv\SOAP\SOAPHandler.cs:Zeile 155.