Using 0.8.0 (and 0.9.0-beta1) it looks like there's a problem with serializing nested structures, the following code (which is a simplified example of what we've got) produces this exception:

Exception: ArgumentException
Message: Field '_field' defined on type 'Example.NestedStruct' is not a field on the target object which is of type 'MsgPack.StreamPacker'.
StackTrace:
at System.Reflection.RtFieldInfo.CheckConsistency(Object target)
at System.Reflection.RtFieldInfo.InternalGetValue(Object obj, StackCrawlMark& stackMark)
at System.Reflection.RtFieldInfo.GetValue(Object obj)
at MsgPack.Serialization.EmittingSerializers.Generated.Example_NestedStructSerializer2.PackValueOf_field(Packer , NestedStruct )
at MsgPack.Serialization.PackHelpers.PackToArray[TObject](PackToArrayParameters1& parameter) at MsgPack.Serialization.EmittingSerializers.Generated.Example_NestedStructSerializer2.PackToCore(Packer , NestedStruct ) at MsgPack.Serialization.MessagePackSerializer1.PackTo(Packer packer, T objectTree)
at MsgPack.Serialization.EmittingSerializers.Generated.Example_OuterClassSerializer1.PackValueOfStruct(Packer , OuterClass )
at MsgPack.Serialization.PackHelpers.PackToArray[TObject](PackToArrayParameters1& parameter) at MsgPack.Serialization.EmittingSerializers.Generated.Example_OuterClassSerializer1.PackToCore(Packer , OuterClass ) at MsgPack.Serialization.MessagePackSerializer1.PackTo(Packer packer, T objectTree)
at MsgPack.Serialization.MessagePackSerializer`1.PackSingleObject(T objectTree)
at Example.Program.Main(String[] args)

using System; using System.Runtime.Serialization; using MsgPack.Serialization; namespace Example { [DataContract] public struct NestedStruct { [DataMember] private int _field; } [DataContract] public class OuterClass { [DataMember] public NestedStruct Struct { get; set; } } class Program { static void Main(string[] args) { var context = new SerializationContext(); context.GetSerializer<OuterClass>().PackSingleObject(new OuterClass()); } } } 

It looks like there's a problem with the generated code, but I'm not sure how to debug that part, sorry. If you change NestedStruct to a class then it works, however.