A quirk in the way .NET serializes objects can lead to intermittent problems when calling Web Services from a .NET CF app. The root cause is that elements in a .NET class are not gaunted returned through reflection in the same order they were entered. The problem only really manifests itself on .NET CF apps, however, because the .NET desktop framework is a bit more predictable (though it isn't required to be). The .NET CF team has a workaround, but a real fix is still pending.