Problem saving and viewing multi-page TIFF

Private Sub btnImport_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnImport.Click

        Dim m_uebGroup As UltraExplorerBarGroup
   	Dim m_pages As Integer
   	Dim m_fi As FileInfo
   	Dim m_di As DirectoryInfo
   	Dim m_srcDoc, m_srcSubDoc As String
   	Dim m_arrFiles As New ArrayList
   	
   	Dim m_tifWriter As TiffWriter
   	Dim m_tifReader As TiffReader
   	Dim m_stream As MemoryStream
   	Dim m_bm As New GraphicsMill.Bitmap
   	Dim m_frame As TiffFrame
   	
   	For Each m_uebGroup In uebImgListBar.Groups
   	    
   	    If m_uebGroup.Items.Count() > 0 Then
   	    
   	        m_srcDoc = Path.Combine(m_srcDirectoryPath, m_uebGroup.Items(0).Tag.ToString())
   	
   	        If File.Exists(m_srcDoc) Then
   	           m_stream = New MemoryStream
   	           
   	            'ensure that all frames in first document are loaded into stream
   	            m_tifWriter = New TiffWriter(m_stream)
   	           
   	            AddFrames(m_tifWriter, m_srcDoc)
   	
   	            'Now check that all frames in documents to be merged with 
   	            'first document are loaded into stream
   	            
   	            m_pages = m_uebGroup.Items.Count
   	            For i As Integer = 1 To m_pages - 1
   	                m_srcSubDoc = Path.Combine(m_srcDirectoryPath, m_uebGroup.Items(i).Tag.ToString())
   	                If File.Exists(m_srcSubDoc) Then
   	                    AddFrames(m_tifWriter, m_srcSubDoc)
   	                    m_arrFiles.Add(m_srcSubDoc)
   	                Else
   	                    'Error
   	                End If
   	            Next
   	
   							'test write to file
                                                        'ERROR occurs on following line
   	            Dim bm_test As New GraphicsMill.Bitmap(m_stream)
   	            bm_test.Save(Path.Combine(m_targetDirectoryPath, Path.ChangeExtension(m_srcDoc, "tif")))
   	            
   	            'TODO: use m_stream.GetBuffer() to save to dbase as BLOB
   	            '..........
End Sub

Private Sub AddFrames(ByRef tw As TiffWriter, ByVal src As String)
    Dim m_tifReader As New TiffReader(src)
    Dim m_bm As New GraphicsMill.Bitmap

    For j As Integer = 0 To m_tifReader.FrameCount - 1
        m_tifReader.LoadFrame(j).GetBitmap(m_bm)
        Dim m_frame As New TiffFrame
        m_frame.Compression = CompressionType.Ccitt4
        m_frame.SetBitmap(m_bm)
        tw.AddFrame(m_frame)
        m_frame.Dispose()
    Next

    m_tifReader.Dispose()
    m_bm.Dispose()
End Sub