ما الخطاء فى هذا الكود - نسخة قابلة للطباعة

PHP كود :
Public Class Form1

    Dim th As New System.Threading.Thread(AddressOf doFind)

    Private Sub TextBox1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox1.TextChanged

        Try
            If (th.ThreadState <> Threading.ThreadState.Unstarted) Then
                th.Abort()
                th = New System.Threading.Thread(AddressOf doFind)
            End If
        Catch ex As Exception

        End Try

        If Not TextBox1.Text.Trim() = "" Then
            th.Start()
        End If

    End Sub

    Sub doFind()
        Dim txtBox As String = Me.TextBox1.Text
        Dim txtLstBox As String

        Me.Invoke(New MethodInvoker(Sub()
                                        Me.FlowLayoutPanel1.Controls.Clear()
                                    End Sub))


        For y As Integer = 0 To Me.ListBox_0.Items.Count - 1

            txtLstBox = Me.ListBox_0.Items.Item(y)
            Dim i As Integer
            i = InStr(txtLstBox, txtBox, CompareMethod.Text)
            If i > 0 Then
                Application.DoEvents()
                Dim itm As New UserControl1
                itm.RichTextBox1.Text = txtLstBox
                '
                If txtBox <> "" Then
                    Me.Invoke(New MethodInvoker(Sub()
                                                    itm.RichTextBox1.SelectionStart = itm.RichTextBox1.Find(txtBox)
                                                    itm.RichTextBox1.SelectionBackColor = Color.Yellow
                                                End Sub))
                End If
                '
                If Me.InvokeRequired Then
                    Me.Invoke(New MethodInvoker(Sub()
                                                    Application.DoEvents()
                                                    Me.FlowLayoutPanel1.Refresh()
                                                    Me.FlowLayoutPanel1.Controls.Add(itm)
                                                    itm.CreateControl()
                                                End Sub))
                End If
            End If
        Next
    End Sub

End Class