To reproduce:
var control =new RadDateTimePickerElement();

ComponentXmlSerializer serializer = new RadTimePickerElement();
StringBuilder xml = new StringBuilder();
StringWriter writer = new StringWriter(xml);
XmlTextWriter xmlWriter = new XmlTextWriter(writer);

xmlWriter.WriteStartElement(control.GetType().FullName);
serializer.WriteObjectElement(xmlWriter, control);
xmlWriter.WriteEndElement();