Port Sharing Enabled Issue with a WCF Net Tcp Service (windows host)

Question

I use the following piece of code to host and start a wcf service using net tcp binding:

public void StartServices()

{

   NetTcpBinding portsharingBinding = new NetTcpBinding();
   portsharingBinding.PortSharingEnabled = true;

   serviceHost = new ServiceHost(intranetDesktopService,new Uri(baseAddress));

   serviceHost.AddServiceEndpoint(typeof(IIntranetDesktopServiceListener),   
        portsharingBinding, endpointAddress);

   serviceHost.Open();

}

However, when I open the service i get the following error: {"The TransportManager failed to listen on the supplied URI using the NetTcpPortSharing service: the service failed to listen."} its a AddressAlreadyInUseException

However the address is not already in use... if I change PortSharingEnabled = true to false.. the service runs fine (but I can only have one instance).

I have enabled the Net.TCP Port sharing service and also addedd the SID of the everyone group to the SMSVChost.config file...

Any ideas?