Serialize a collection of objects

[Edneeis]

Either it needs an XMLArray attribute for that property or its because you are exposing it as an item property of a non-collection. If its the latter try changing it to this:

Public ReadOnly Property InvoiceItems() As InvoiceItemCollection
        Get
            Return InvItems
        End Get
    End Property

Or it might need both, not sure.

And if you don't want to allow the user to add items then you can handle that in the InvoiceItemsCollection itself.