.NET

When calling the following register function :

EslClient eslClient = new EslClient(apikey, apiUrl);
eslClient.EventNotificationService.Register(
                EventNotificationConfigBuilder.NewEventNotificationConfig(callBackUrl)
                .ForEvent(NotificationEvent.SIGNER_COMPLETE).ForEvent(NotificationEvent.PACKAGE_DELETE));

I am getting: System.NullReferenceException: Object reference not set to an instance of an object. This is happening on our development machines but our actual live application is running just fine, this error just propped up today.