gistfile1.cs

		[Fact] //this is a the test attribute when using xUnit
		public void When_xml_Something_Then_serialize_returns_null()
		{
			string serializedObject =
				"<?xml version=\"1.0\" encoding=\"utf-8\"?><MyClass xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns=\"http://exampleA.org\" />";
			using (var stringReader = new StringReader(serializedObject))
			{
				Assert.Null(new XmlSerializer(typeof(MyClass)).Deserialize(stringReader));
			}
		}


[Fact]
public void When_xml_Then_serialize_returns_null_with_xml_reader()
{
	string serializedObject =
				"<?xml version=\"1.0\" encoding=\"utf-8\"?><MyClass xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns=\"http://exampleA.org\" />";
			using (var stringReader = new StringReader(serializedObject))
			{
				var doc = new XmlDocument();
				doc.Load(stringReader);
				Assert.Null(new XmlSerializer(typeof(MyClass)).Deserialize(stringReader));
			}
		}

//---------------------------


	[Serializable]
	[XmlRoot(Namespace = "http://example.org")]
	public class MyClass
	{
	}

the test throws

System.InvalidOperationException: was not expected.
at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReaderMyClass.Read3_MyClass()
System.InvalidOperationException: There is an error in XML document (1, 40).

if you change the xmlns:xsd or the xmlns:xsi then the class is deserialized no probs