InvalidOperationException on GetType - vb.net

Question

I try to serialize a Class in VB using XMLSerializer.
But when I call GetType for my Class I got a InvalidOperationException error.
Dim Playlist_serialize As New XmlSerializer(p.GetType)
Here is my class :
Public Class Playlist
Private p_name As String
Private p_elements As List(Of Playlist_element)
Sub New()
p_elements = New List(Of Playlist_element)
End Sub
Public Property Name() As String
Get
Name = p_name
End Get
Set(value As String)
p_name = value
End Set
End Property
Public Property Elements() As List(Of Playlist_element)
Get
Elements = p_elements
End Get
Set(value As List(Of Playlist_element))
p_elements = value
End Set
End Property
Here is my Playlist_element :
Public Class Playlist_element
Private p_Name As String
Private p_Type As String
Private p_Genre As String
Public Property Name() As String
Get
Name = p_Name
End Get
Set(value As String)
p_Name = value
End Set
End Property
Public Property Type() As String
Get
Type = p_Type
End Get
Set(value As String)
p_Type = value
End Set
End Property
Public Property Genre() As String
Get
Genre = p_Genre
End Get
Set(value As String)
p_Genre = value
End Set
End Property
Sub New(ByVal name As String, ByVal type As String, ByVal genre As String)
Me.Name = name
Me.Genre = genre
Me.Type = Type
End Sub
End Class

Answer 1

There are several issues with the way Playlist_element is coded. First your property getters are wrong. They need to return the backing field:
Public Property Name() As String
Get
' this does nothing:
'Name = p_Name
Return p_Name
End Get
Set(value As String)
p_Name = value
End Set
End Property
Next, I would not use Type as a property name even if you can. If you drill into the inner exception and view the message, it tells you that it cannot serialize PlayList_element because it does not have a simple constructor. All serializers require this because they do not know how to use:
Sub New(ByVal name As String, ByVal type As String, ByVal genre As String)
p_Name = name
p_Genre = genre
p_Type = type
End Sub
' add:
Public Sub New()
End Sub
It should work fine. I should note that as of VS2010, you can use auto-implemented properties and skip a lot of that code:
Public Class Element
Public Property Name() As String
Public Property Type() As String
Public Property Genre() As String
Sub New(name As String, type As String, genre As String)
_Name = name
_Genre = genre
_Type = type
End Sub
Public Sub New()
End Sub
End Class
VS provides a "hidden" backing field as with _Name, _Genre etc.