I have a CRC32 method which is like this:

        Public cFileName As String = ""
        Public nCRC32 As Integer = 0
        Private nBufferSize As Integer = 1024
        Private nCRC32Table() As Integer

        ' This is the official polynomial used by CRC32 in PKZip.
        ' Often the polynomial is shown reversed (04C11DB7).
        Private Sub Init()
            Dim lnDWPolynomial As Integer = &HEDB88320
            Dim lnCounter As Integer = 0
            Dim lnCounter2 As Integer = 0
            ReDim nCRC32Table(256)
            Dim lnDWCRC As Integer

            For lnCounter = 0 To 255
                lnDWCRC = lnCounter
                For lnCounter2 = 8 To 1 Step -1
                    If (lnDWCRC And 1) Then
                        lnDWCRC = ((lnDWCRC And &HFFFFFFFE) \ 2&) And &H7FFFFFFF
                        lnDWCRC = lnDWCRC Xor lnDWPolynomial
                    Else
                        lnDWCRC = ((lnDWCRC And &HFFFFFFFE) \ 2&) And &H7FFFFFFF
                    End If
                Next
                nCRC32Table(lnCounter) = lnDWCRC
            Next

        End Sub

        ' This is the main method to call
        Public Function GetCRC() As Boolean
            Dim loStream As Stream
            loStream = New FileStream(cFileName, FileMode.Open, FileAccess.Read, FileShare.Read, 8192)
            nCRC32 = GetCrc32(loStream)
            loStream.Close()
            Return True
        End Function

        Private Function GetCrc32(ByRef toStream As System.IO.Stream) As Integer
            Dim lnCRC32Result As Integer = &HFFFFFFFF
            Dim loBuffer(nBufferSize) As Byte
            Dim lnReadSize As Integer = nBufferSize
            Dim lnCount As Integer = 0
            Dim lnCounter As Integer = 0
            Dim lnLookup As Integer = 0

            lnCount = toStream.Read(loBuffer, 0, lnReadSize)
            Do While lnCount > 0
                For lnCounter = 0 To lnCount - 1
                    lnLookup = (lnCRC32Result And &HFF) Xor loBuffer(lnCounter)

                    ' Nasty shr 8 with vb :/
                    lnCRC32Result = ((lnCRC32Result And &HFFFFFF00) \ &H100) And 16777215

                    lnCRC32Result = lnCRC32Result Xor nCRC32Table(lnLookup)
                Next
                lnCount = toStream.Read(loBuffer, 0, lnReadSize)
            Loop
            Return Not lnCRC32Result
        End Function

This method has always worked well. However, tonight, on a specific JPG, it returns:

"Object reference not set to an instance of an object."

This is in regards to the line:

                    lnCRC32Result = lnCRC32Result Xor nCRC32Table(lnLookup)

I really don't understand how this line could return an object reference not set. Anyone would have any idea and also about what is causing this?