XmlObjectSerializer.WriteStartObject Method (XmlWriter, Object)
Writes the start of the object's data as an opening XML element using the specified XmlWriter.
Assembly: System.Runtime.Serialization (in System.Runtime.Serialization.dll)
The type being serialized does not conform to data contract rules. For example, the DataContractAttribute attribute has not been applied to the type.
There is a problem with the instance being serialized.
The maximum number of objects to serialize has been exceeded. Check the MaxItemsInObjectGraph property.