[DataContract]
public class Setting : ConfigurationElement, ICloneable
{

    [DataMember]
    [ConfigurationProperty("type")]
    public string Type
    {
        get { return (string)this["type"]; }
        set { this["type"] = value; }
    }
}

"Type 'Imaging.Setting' cannot inherit from a type that is not marked with DataContractAttribute or SerializableAttribute.  Consider marking the base type 'System.Configuration.ConfigurationElement' with DataContractAttribute or SerializableAttribute, or removing them from the derived type."