getting started with .net sdk and api part 2

I have the same problem like "mlawson" at http://communities.vmware.com/message/2190842

If I execute one of the sample programs (i.e. HellovCloud), I get the following error:

VCloudRuntimeException: The given header was not found

The error occurs when the login methode has been called:

client.Login(username, password);

I did not changed anything of the sample code.

The parameters for:

public static void Login(string vCloudURL, string username, string password)
        {
            try
            {
                client = new vCloudClient(vCloudURL, com.vmware.vcloud.sdk.constants.Version.V5_1);
                //client = new vCloudClient(vCloudURL);
                client.Login(username, password);

                                   ...

are the following

vcloudURL = https://vcloud..

username = user@System

password = password

The credentials should be ok and are the same like logging in via http at vcloud (version 5.1.0.810718).

The exception is catched at:

catch (Exception e)
            {
                Logger.Log(TraceLevel.Critical, e.Message);
                Console.WriteLine(e.Message);
            }

Thanks in advance for any help.