Under Silverlight only public types may be serialized with the DataContractSerializer. If you want to make your data classes internal to your assembly and serialise them for use in a WCF service you will find that the service call will fail at runtime with a SecurityException inside a misleading exception about inability to communicate with the service. There is a workaround however which involves exposing your internal types to the Silverlight base class libraries with the InternalsVisibleTo attribute. Simply add the following code to your AssemblyInfo.cs file:-
- [assembly: InternalsVisibleTo("System.Runtime.Serialization, PublicKey=00240000048000009400000006020000002400005253413100040000010001008d56c76f9e8649383049f383c44be0ec204181822a6c31cf5eb7ef486944d032188ea1d3920763712ccb12d75fb77e9811149e6148e5d32fbaab37611c1878ddc19e20ef135d0cb2cff2bfec3d115810c3d9069638fe4be215dbf795861920e5ab6f7db2e2ceef136ac23d5dd2bf031700aec232f6c6b1c785b4305c123b37ab")]
If you use the DataContractJsonSerializer you must also add the System.Servicemodel.Web assembly (the public key is the same).