HTTP access denied for .NET application

[gbp3791]

I'm having an issue with an application (using .NET 4.6) that hosts a local web server on a configurable HTTP port. I'm unable to run that server due to what seems a permissions issue. Hoping someone has a quick fix but I haven't found any after some searching. Below is the exception capture, using port 3333 (same error for default 8080):

System.ServiceModel.AddressAccessDeniedException: HTTP could not register URL http://+:3333/GLGW/GWServices_v1/Messages.svc/. Your process does not have access rights to this namespace (see http://go.microsoft.com/fwlink/?LinkId=70353 for details). ---> System.Net.HttpListenerException: Access denied
at System.Net.HttpListener.SetupV2Config()
at System.Net.HttpListener.Start()
at System.ServiceModel.Channels.SharedHttpTransportManager.OnOpen()
--- End of inner exception stack trace ---
at SkyWave.Messenger.WebServiceUtility.OpenWebServiceHost(Object singletonInstance, String url, ServiceAuthorizationManager serviceAuthorizationManager, Type webServiceHostType)
at SkyWave.ModemSimulator.ModemSimulatorForm.StartGatewayWebService()

Inner exception:

System.Net.HttpListenerException (0x80004005): Access denied
at System.Net.HttpListener.SetupV2Config()
at System.Net.HttpListener.Start()
at System.ServiceModel.Channels.SharedHttpTransportManager.OnOpen()

[DarkShadow44]

What program is this about, can we test it directly?