Web Method return a complex class

[jeytu]

Hi all,
I'm a newbie with .net. I have created a web method that would return a class.
The definition of the class is
<Serializable() > Public Class Response
Dim l_status As Boolean
Dim l_Message As New ArrayList
Public Property Status() As Boolean
Get
Status = l_status
End Get
Set(ByVal Value As Boolean)
l_status = Value
End Set
End Property
Public Property Messages() As ArrayList
Get
Messages = l_Message
End Get
Set(ByVal Value As ArrayList)
l_Message = Value
End Set
End Property
Dim lbooks As New Books
Public Property mybooks() As Books
Get
mybooks = lbooks
End Get
Set(ByVal Value As Books)
lbooks = Value
End Set
End Property
End Class

Wherein Books is a collection of class Book.

When invoking the webmethod that returns the Response class, I get a "System.Invalid OperationExcept ion: Request format is unrecognized" error, if the class Response has some value for Books. But if it is just an Arraylist, it's okay.
Would somebody help me, what is wrong with my class definition? Thanks.

<Serializable() > _
Public Class Book
Private mName As String
Public Sub New(ByVal bookName As String)
mName = bookName
End Sub

Public Property Name() As String
Get
Return mName
End Get
Set(ByVal Value As String)
mName = Value
End Set
End Property
End Class

<Serializable() > _
Public Class Books
Implements IEnumerable
Private mList As New ArrayList

Public Sub Add(ByVal bk As System.Object)
bk = DirectCast(bk, Book)
mList.Add(bk)
End Sub

Default Public ReadOnly Property List(ByVal index As Integer) As Book
Get
Return DirectCast(mLis t(index), Book)
End Get
End Property

Public Function GetEnumerator() As System.Collecti ons.IEnumerator Implements System.Collecti ons.IEnumerable .GetEnumerator
Return New BooksEnumerator (mList)
End Function

Class BooksEnumerator
Implements IEnumerator
Private index As Integer = -1
Private mList As ArrayList

Friend Sub New(ByVal list As ArrayList)
mList = list
End Sub
Public ReadOnly Property Current() As Object Implements System.Collecti ons.IEnumerator .Current
Get
Return mList(index)
End Get
End Property
Public Function MoveNext() As Boolean Implements System.Collecti ons.IEnumerator .MoveNext
If index < mList.Count - 1 Then
index += 1
Return True
Else
Return False
End If
End Function
Public Sub Reset() Implements System.Collecti ons.IEnumerator .Reset
index = 0
End Sub
End Class
End Class