weird null pointer exception from VB code - vb.net

Question

I am using Windows Vista x64 + VSTS 2008. I am debugging the sample program from the following URL (associated sample code for this article),
http://www.codeproject.com/KB/audio-video/CaptureScreenAsVideo.aspx?display=PrintAll&fid=129831&df=90&mpp=25&noise=3&sort=Position&view=Quick&fr=101&select=1160633
But I met with null pointer exception when press the write to file button, here is my screen snapshot.
http://tinypic.com/view.php?pic=14cbfop&s=5
Any ideas what is wrong?
EDIT1: here is the whole source code.
Imports WMEncoderLib
Imports WMPREVIEWLib
Imports System.IO
Public Class Form1
Inherits System.Windows.Forms.Form
#Region " Windows Form Designer generated code "
Public Sub New()
MyBase.New()
'This call is required by the Windows Form Designer.
InitializeComponent()
'Add any initialization after the InitializeComponent() call
End Sub
'Form overrides dispose to clean up the component list.
Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
If disposing Then
If Not (components Is Nothing) Then
components.Dispose()
End If
End If
MyBase.Dispose(disposing)
End Sub
'Required by the Windows Form Designer
Private components As System.ComponentModel.IContainer
'NOTE: The following procedure is required by the Windows Form Designer
'It can be modified using the Windows Form Designer.
'Do not modify it using the code editor.
Friend WithEvents Button1 As System.Windows.Forms.Button
<System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
Me.Button1 = New System.Windows.Forms.Button
Me.SuspendLayout()
'
'Button1
'
Me.Button1.Location = New System.Drawing.Point(48, 80)
Me.Button1.Name = "Button1"
Me.Button1.Size = New System.Drawing.Size(216, 23)
Me.Button1.TabIndex = 1
Me.Button1.Text = "Write To file and Close application"
'
'Form1
'
Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
Me.ClientSize = New System.Drawing.Size(292, 266)
Me.Controls.Add(Me.Button1)
Me.Name = "Form1"
Me.Text = "Form1"
Me.ResumeLayout(False)
End Sub
#End Region
Dim Encoder As WMEncoder
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
' Create a WMEncoder object.
Encoder = New WMEncoder
' Retrieve the source group collection and add a source group.
Dim SrcGrp As IWMEncSourceGroup2
Dim SrcGrpColl As IWMEncSourceGroupCollection
SrcGrpColl = Encoder.SourceGroupCollection
SrcGrp = SrcGrpColl.Add("SG_1")
' Add a video and audio source to the source group.
Dim SrcVid As IWMEncVideoSource2
Dim SrcAud As IWMEncAudioSource
SrcVid = SrcGrp.AddSource(WMENC_SOURCE_TYPE.WMENC_VIDEO)
SrcAud = SrcGrp.AddSource(WMENC_SOURCE_TYPE.WMENC_AUDIO)
' Identify the source files to encode.
SrcVid.SetInput("ScreenCap://ScreenCapture1")
SrcAud.SetInput("Device://Default_Audio_Device")
' Choose a profile from the collection.
Dim ProColl As IWMEncProfileCollection
Dim Pro As IWMEncProfile
Dim i As Integer
Dim lLength As Long
ProColl = Encoder.ProfileCollection
lLength = ProColl.Count
'For i = 0 To lLength - 1
' Console.WriteLine(ProColl.Item(i).Name)
'Next
For i = 0 To lLength - 1
Pro = ProColl.Item(i)
If Pro.Name = "Windows Media Video 8 for Local Area Network (384 Kbps)" Then
SrcGrp.Profile = Pro
Exit For
End If
Next
' Fill in the description object members.
Dim Descr As IWMEncDisplayInfo
Descr = Encoder.DisplayInfo
Descr.Author = "Armoghan Asif"
Descr.Copyright = "Copyright information"
Descr.Description = "Text description of encoded content"
Descr.Rating = "Rating information"
Descr.Title = "Title of encoded content"
' Add an attribute to the collection.
Dim Attr As IWMEncAttributes
Attr = Encoder.Attributes
Attr.Add("URL", "www.adnare.com")
' Specify a file object in which to save encoded content.
Dim File As IWMEncFile
File = Encoder.File
File.LocalFileName = "C:\OutputFile.avi"
' Crop 2 pixels from each edge of the video image.
SrcVid.CroppingBottomMargin = 2
SrcVid.CroppingTopMargin = 2
SrcVid.CroppingLeftMargin = 2
SrcVid.CroppingRightMargin = 2
' Start the encoding process.
Encoder.Start()
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
If Encoder.RunState Then
Encoder.Stop()
Application.Exit()
End If
End Sub
End Class

Answer 1

Did you install Windows Media Encoder 9 Series and SDK as instructed by the article? My guess is that this is the culprit.

Answer 2

You probably don't have the encoder. Check the prerequisites (See this line: "You will be needing Windows Media Encoder 9 Series and SDK.").

Answer 3

Is this code still intact?
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
' Create a WMEncoder object.
Encoder = New WMEncoder
The implication is that that code is missing or quietly failing.
If you put a breakpoint on the line following Encoder = New WMEncoder, what's the value of Encoder?