Fault Exception windows phone connecting to WCF WP8 - windows

Question

I have created a WCF which I then created a WP8 application and added the service reference. The error is "An exception of type 'System.ServiceModel.FaultException' occurred in System.ServiceModel.ni.dll but was not handled in user code"
If anyone could possible give me some indication as I have googled this and found nothing the same.
The error comes up here
public void EndAddUser(System.IAsyncResult result)
{
object[] _args = new object[0];
base.EndInvoke("AddUser", _args, result);
}
My main classes:
public partial class MainPage : PhoneApplicationPage
{
private Service1Client _serviceClient;
// Constructor
public MainPage()
{
InitializeComponent();
_serviceClient = new Service1Client();
_serviceClient.LoginUserCompleted += new
}
private void loginBtn_Click(object sender, RoutedEventArgs e)
{
_serviceClient.LoginUserAsync(userNameTxtBox.Text, passwordTxtBox.Text);
}
private void newAccountBtn_Click(object sender, RoutedEventArgs e)
{
this.NavigationService.Navigate(new Uri("/AddAccount.xaml", UriKind.Relative));
}
private void _serviceClient_LoginUserCompleted(object senter,
LoginUserCompletedEventArgs e)
{
if (e.Error == null && e.Result != null)
{
MessageBox.Show("Welcome " + e.Result + "!");
}
else
{
MessageBox.Show("Could not log in. Please check user name/password and try
again.");
}
}
}
public partial class AddAccount : PhoneApplicationPage
{
private Service1Client _serviceClient;
public AddAccount()
{
InitializeComponent();
_serviceClient = new Service1Client();
_serviceClient.AddUserCompleted += new EventHandler<AsyncCompletedEventArgs>
(_serviceClient_AddUserCompleted);
}
private void addAccountBtn_Click(object sender, RoutedEventArgs e)
{
_serviceClient.AddUserAsync(fullnameTxtBox.Text, userNameTxtBox.Text,
passwordTxtBox.Text);
}
void _serviceClient_AddUserCompleted(object sender, AsyncCompletedEventArgs e)
{
if (e.Error == null)
{
MessageBox.Show("User account created. Please login");
this.NavigationService.GoBack();
}
else
{
MessageBox.Show("User account could not be added, Please try again");
}
}
}