{"<user xmlns=''> was not expected.} Deserializing Twitter XML

Either decorate your root entity with the XmlRoot attribute which will be used at compile time.

[XmlRoot(Namespace = "www.contoso.com", ElementName = "MyGroupName", DataType = "string", IsNullable=true)]

Or specify the root attribute when de serializing at runtime.

XmlRootAttribute xRoot = new XmlRootAttribute();
xRoot.ElementName = "user";
// xRoot.Namespace = "http://www.cpandl.com";
xRoot.IsNullable = true;

XmlSerializer xs = new XmlSerializer(typeof(User),xRoot);

Even easier is just to add the following annotations to the top of your class:

[Serializable, XmlRoot("user")]
public partial class User
{
}

XmlSerializer xs = new XmlSerializer(typeof(User), new XmlRootAttribute("yourRootName")); 

The error message is so vague, for me I had this code:

var streamReader = new StreamReader(response.GetResponseStream());
var xmlSerializer = new XmlSerializer(typeof(aResponse));
theResponse = (bResponse) xmlSerializer.Deserialize(streamReader);

Notice xmlSerializer is instantiated with aResponse but on deserializing I accidentally casted it to bResonse.

The simplest and best solution is just to use XMLRoot attribute in your class, in which you wish to deserialize.

Like:

[XmlRoot(ElementName = "YourPreferableNameHere")]
public class MyClass{
...
}

Also, use the following Assembly :

using System.Xml.Serialization;