I'm attempting to deserialize a Codification object but it throws the following error.

Object reference not set to an instance of an object.

at Accord.Collections.TwoWayDictionary`2.OnDeserialized(StreamingContext context) in D:\Accord.NET.3.2.0\Sources\Accord.Core\Collections\TwoWayDictionary.cs:line 457
at System.Runtime.Serialization.SerializationEventHandler.Invoke(StreamingContext context)
at System.Runtime.Serialization.ObjectManager.RaiseDeserializationEvent()
at System.Runtime.Serialization.Formatters.Binary.ObjectReader.Deserialize(HeaderHandler handler, __BinaryParser serParser, Boolean fCheck, Boolean isCrossAppDomain, IMethodCallMessage methodCallMessage)
at System.Runtime.Serialization.Formatters.Binary.BinaryFormatter.Deserialize(Stream serializationStream, HeaderHandler handler, Boolean fCheck, Boolean isCrossAppDomain, IMethodCallMessage methodCallMessage)
at System.Runtime.Serialization.Formatters.Binary.BinaryFormatter.Deserialize(Stream serializationStream)

Here's the code I'm using to deserialize:

            fs = New FileStream(Application.StartupPath & "\cb.dat", FileMode.Open)
            bf = New BinaryFormatter()
            codebook = CType(bf.Deserialize(fs), Codification)
            fs.Close()

And what I am using to serialize:

            fs = New FileStream(Application.StartupPath & "\cb.dat", FileMode.CreateNew)
            bf = New BinaryFormatter()
            bf.Serialize(fs, codebook)
            fs.Close()

I'm able to successfully serialize/deserialize the NaiveBayes and DataTable objects with the same code so I don't believe that's the issue.