问在VB.NET中读取文件错误？

EN

Private Sub readusersdata(ByVal userdatafile As String)
    ListView1.BeginUpdate()
    ListView1.Items.Clear()
    Using snxl As IO.Stream = IO.File.Open(userdatafile, IO.FileMode.Open)

        Using str As New IO.StreamReader(snxl)
            str.BaseStream.Position = 4
            Dim usersm As Integer = str.BaseStream.ReadByte()
            Dim users As Integer = usersm
            While users > 0
                If usersm = users Then
                    Dim trailtouser As Integer = 0
                    str.BaseStream.Position = 6
                    Dim ust As Integer = str.BaseStream.ReadByte()
                    str.BaseStream.Position = 8
                    Dim snb(ust - 1) As Char
                    str.ReadBlock(snb, 0, ust)
                    Dim bst = New String(snb)
                    If usersm = 1 Then
                        str.BaseStream.Position = 16
                    Else
                        str.BaseStream.Position = 15
                    End If
                    cLVN(ListView1, bst, str.BaseStream.ReadByte)
                    str.BaseStream.Position = 8 + snb.Length
                    str.BaseStream.Position += str.BaseStream.ReadByte + 1
                Else

                    Dim usn As Integer = str.BaseStream.ReadByte
                    str.BaseStream.Position += 2
                    Dim chrpos As Integer = str.BaseStream.Position
                    Dim xnl(usn - 1) As Char
                    str.Read(xnl, 0, usn - 1)
                    Dim skpbyte As Integer = str.BaseStream.ReadByte
                    str.BaseStream.Position += 3
                    Dim udata As Integer = str.BaseStream.ReadByte


                End If

                users -= 1

            End While
        End Using
    End Using
    ListView1.EndUpdate()
End Sub