the last line cannot be highlighted

[eyein]

i've created a program which will compare 2 richtextboxes;where will highlight the line error in both richtexbox.the programme can be run;but the last line doesnt being highlight...e.g: there are 6 errors,but only 5 errors being highlighted,and the sixth line cannot be highlighted.does someone know where my mistakes are?below is my COMPARE programmes :~

Dim i As Integer, startindex As Integer = 0
        Dim where As String, array1() As String = richtextbox1.Lines, array2() As String = RichTextBox2.Lines
        For i = 0 To UBound(array1)
            If String.Compare(array1(i), array2(i), False) = 0 Then
                RichTextBox3.Text = RichTextBox3.Text & " ****************** " & vbNewLine
            ElseIf String.Compare(array1(i), array2(i), True) = 1 Then
                RichTextBox3.Text = RichTextBox3.Text & "error line " & "(" & i + 1 & ")" & " : " & array1(i) & vbNewLine
                Dim endindex As Integer = array1(i).Length
                where = InStr(richtextbox1.Text, array1(i))
                richtextbox1.SelectionColor = Color.DeepPink
                richtextbox1.Select(startindex, endindex)
                richtextbox1.SelectionStart = where - 1
                richtextbox1.SelectionLength = Len(array1(i))
            ElseIf String.Compare(array2(i), array1(i), True) = 1 Then
                RichTextBox3.Text = RichTextBox3.Text & "error line " & "(" & i + 1 & ")" & " : " & array2(i) & vbNewLine
                Dim endindex2 As Integer = array2(i).Length
                where = InStr(RichTextBox2.Text, array2(i))
                RichTextBox2.SelectionColor = Color.Yellow
                RichTextBox2.Select(startindex, endindex2)
                RichTextBox2.SelectionStart = where - 1
                RichTextBox2.SelectionLength = Len(array2(i))
            End If
        Next i