Solved the problem...
One of the things that cheated me the most, was that the AXIS camera and the Client (PC) had to be time synchronous within +-5 sec. If I change the PC time, I just get the 400 bad request back. If the time matches everything works!!!
DateTime UTCTime = DateTime.UtcNow;
tbInfo.AppendText(string.Format("Client Local Time: {0}\n", DateTime.Now.ToString("HH:mm:ss")));
tbInfo.AppendText(string.Format("Client UTC Time: {0}\n", UTCTime.ToString("HH:mm:ss")));
tbInfo.AppendText("\n\n");
HttpTransportBindingElement httpTransport = new HttpTransportBindingElement();
TransportSecurityBindingElement transportSecurity = new TransportSecurityBindingElement();
transportSecurity.EndpointSupportingTokenParameters.SignedEncrypted.Add(new UsernameTokenParameters());
transportSecurity.AllowInsecureTransport = true;
transportSecurity.IncludeTimestamp = false;
TextMessageEncodingBindingElement textMessageEncoding = new TextMessageEncodingBindingElement(MessageVersion.Soap12, Encoding.UTF8);
CustomBinding binding = new CustomBinding(transportSecurity, textMessageEncoding, httpTransport);
EndpointAddress serviceAddress = new EndpointAddress(addressDirect);
ChannelFactory<Device> channelFactory = new ChannelFactory<Device>(binding, serviceAddress);
UsernameClientCredentials credentials = new UsernameClientCredentials(new UsernameInfo(username, password));
channelFactory.Endpoint.Behaviors.Remove(typeof(ClientCredentials));
channelFactory.Endpoint.Behaviors.Add(credentials);
Device channel = channelFactory.CreateChannel();
var unitTime = channel.GetSystemDateAndTime(new GetSystemDateAndTimeRequest());
tbInfo.AppendText(string.Format("Camera Local Time: {0}:{1}:{2}\n", unitTime.SystemDateAndTime.LocalDateTime.Time.Hour, unitTime.SystemDateAndTime.LocalDateTime.Time.Minute, unitTime.SystemDateAndTime.LocalDateTime.Time.Second));
tbInfo.AppendText(string.Format("Camera UTC Time: {0}:{1}:{2}\n", unitTime.SystemDateAndTime.UTCDateTime.Time.Hour, unitTime.SystemDateAndTime.UTCDateTime.Time.Minute, unitTime.SystemDateAndTime.UTCDateTime.Time.Second));
var info = channel.GetDeviceInformation(new GetDeviceInformationRequest());
MessageBox.Show(string.Format("Model: {0}", info.Model));