because your base class doesn't support serialization, try to implement ISerializable interface, seeCustom Serialization
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/html/cpconCustomSerialization.asp
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/html/cpconCustomSerialization.asp
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