(NullReferenceException) - Object reference not set to an instance of an object.

Question

Ofcourse I have read plenty of other topics about people having this kind of problem but they all didnt seem to work for me. A common cause was when a object was not Dim'ed As New. Or when object was Nothing/null.

However my code is nothing like this I believe. Here's my code that causes the exception:

Code Snippet

Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        Dim fs2 As New FileStream("names.txt", FileMode.OpenOrCreate, FileAccess.ReadWrite)
        Dim sr2 As New StreamReader(fs2)
        Dim NameIsPresent As Boolean = False
        Dim NoLine As String = ""
        Dim PrevLine As String = ""
        Dim CurLine As String = ""

        ListBox1.Items.Clear()

        Do While sr2.Peek <> -1
            PrevLine = sr2.ReadLine()
            CurLine = sr2.ReadLine()
            NoLine = sr2.ReadLine()
            If CurLine.StartsWith(TextBox1.Text) Then ListBox1.Items.Add(PrevLine)
            If CurLine = TextBox1.Text And PrevLine = TextBox2.Text Then
                NickIsPresent = True
            End If
        Loop

        If NameIsPresent = False Then
            Dim sw As StreamWriter
            sr2.Close()
            sw = File.AppendText("Names.txt")
            sw.Write(TextBox2.Text)
            sw.Write(TextBox1.Text)
            sw.Write("")
            sw.Flush()
        End If
    End Sub

What this code should do is read a textfile to check if the name(textbox2.text) is present in it. Then if it is not, it should add the name and address of the person to the text file. Also the code should place names with same address in listbox1.
Sounds easy but a keep getting the error. Could somebody provide me with a working code sample because this "NullReferenceException -  Object reference not set to an instance of an object" is really confusing me.

Thanks in advance!