Service_InternalServerError on new User creation

Howdy folks,

I am trying to get a new application up with AAD as the default backend identity provider. Crawling through the various samples and examples, and trying to use the latest set of libraries, I have run into a snag in terms of creating new users with the latest libraries. (If I use the older libraries it works fine).  

when using Microsoft.Azure.ActiveDirectory.GraphClient 2.0.1

try
            {
                AuthenticationContext authContext = new AuthenticationContext(authority);
                ClientCredential credential = new ClientCredential(clientId, appKey);
                ActiveDirectoryClient graphConnection = new ActiveDirectoryClient(new Uri(new Uri(graphResourceId),tenant), async () =>
                {
                    var result = authContext.AcquireToken(graphResourceId, credential);
                    return result.AccessToken;
                });
                Microsoft.Azure.ActiveDirectory.GraphClient.User newAzureUser = new Microsoft.Azure.ActiveDirectory.GraphClient.User();
                newAzureUser.GivenName = User.FirstName;
                newAzureUser.Surname = User.LastName;
                newAzureUser.UserPrincipalName = User.FirstName + "." + User.LastName+"@"+tenant;
                newAzureUser.DisplayName = User.FirstName + User.LastName;
                newAzureUser.AccountEnabled = true;

                newAzureUser.PasswordProfile = new PasswordProfile
                {
                    ForceChangePasswordNextLogin = true,
                    Password = User.UserPassword

                };
                graphConnection.Users.AddUserAsync(newAzureUser).Wait();

At this point, an exception is raised with an 500 internal server error, no hint as to what's wrong.

If I revert to the 1.0.3 version and use:

AuthenticationContext authContext = new AuthenticationContext(Startup.Authority);
                ClientCredential credential = new ClientCredential(clientId, appKey);
                result = authContext.AcquireToken(graphResourceId, credential);
Guid ClientRequestId = Guid.NewGuid();
                GraphSettings graphSettings = new GraphSettings();
                graphSettings.ApiVersion = GraphConfiguration.GraphApiVersion;
                GraphConnection graphConnection = new GraphConnection(result.AccessToken, ClientRequestId, graphSettings);
                graphConnection.Add(user);

Then it all goes through nicely. Now while I could obviously use the older version, I would prefer to use the latest to ensure tech debt is minimised. Is there something I have done that is stupid and cant spot myself, or is the problem a little deeper?

Thanks in advance