DataContractSerializer and Dictionary<string,object> fails when reading

Try using the KnownTypeAttribute so that DataContractSerializer knows about the List<string> type. Unfortunately, that seems to go against your idea of not having to know about the types before hand.

I'm basing this on the following code, which uses DataContractSerializer to serialize a Dictionary<string, object> containing List<string>:

Dictionary<string,object> dictionary = new Dictionary<string, object>();

dictionary.Add("k1", new List<string> { "L1", "L2", "L3" });

List<Type> knownTypes = new List<Type> { typeof(List<string>) };
DataContractSerializer serializer = new DataContractSerializer(typeof(Dictionary<string,object>), knownTypes);
MemoryStream stream = new MemoryStream();

serializer.WriteObject(stream, dictionary);

StreamReader reader = new StreamReader(stream);

stream.Position = 0;
string xml = reader.ReadToEnd();

If you knownTypes is not provided to the DataContractSerializer, it throws an exception.

SerializationException: Type 'System.Collections.Generic.List`1[[System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]' with data contract name 'ArrayOfstring:http://schemas.microsoft.com/2003/10/Serialization/Arrays' is not expected. Consider using a DataContractResolver or add any types not known statically to the list of known types - for example, by using the KnownTypeAttribute attribute or by adding them to the list of known types passed to DataContractSerializer.