Using Sleep in VB.NET - vb.net

Question

I have a kind of simple issue, I have a section of code that sends out a test email and just before this process occurs, I'd like a marquee progress bar to appear, indicating that something is happening.
However, the progress bar does not appear until the test email has been sent.
I've tried experimenting with the Sleep function, but the progress bar still wont appear until after the test email sends.
Does anyone know why?
Code: (Note: GroupBoxTesting contains the Progress bar)
Private Sub BTMsendmailtest_Click_1(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BTMsendmailtest.Click
GroupBoxTesting.Visible = True
Threading.Thread.Sleep(500)
Try
Dim Mail As New MailMessage
Mail.Subject = "Test email for Email Alerts!"
Mail.To.Add(TXTemailaddy.Text)
Mail.From = New MailAddress(TXTsmtpusr.Text)
Mail.Body = "This is a test message from Email Alerts!" & Environment.NewLine & Environment.NewLine & "If you are reading this, then Email Alerts! is properly configured."
Dim SMTP As New SmtpClient(TXTsmtpsvr.Text)
If CHKEnableSSL.Checked = True Then
SMTP.EnableSsl = True
Else
SMTP.EnableSsl = False
End If
SMTP.Credentials = New System.Net.NetworkCredential(TXTsmtpusr.Text, TXTsmtppwd.Text)
SMTP.Port = TXTsmtpport.Text
SMTP.Send(Mail)
SendingPB.Value = False
MessageBox.Show("A test email has been sent to " & TXTemailaddy.Text & " from " & TXTsmtpusr.Text & "." & Environment.NewLine & Environment.NewLine & "If you did not recieve an email, please check your settings and try again.", "Test Email")
GroupBoxTesting.Visible = False
Catch ex1 As Exception
SendingPB.Value = False
GroupBoxTesting.Visible = False
MessageBox.Show(ex1.Message)
Return
End Try
End Sub

Answer 1

You've told the UI thread (which is the thread your code as it is is currently running on) to go to sleep, so it goes to sleep and doesn't do anything for the specified time. Even without the Sleep, it may be that the UI thread is too busy sending the email to update the display of the marquee progress bar.
You could either use a BackgroundWorker to send the email, or use the SmtpClient.SendAsync Method. The latter includes an example; there is another example at How do I send email asynchronously?.

Answer 2

I had the error using Excel Automation with a VB.Net application while processing and writing over 20,000 rows. I used this code to resolve the issue.
' ---- Write the Row to the Worksheet
Threading.Thread.Sleep(1000)
lstrStartingColRow = "A" & mlngIdx.ToString
If .InsertArrayIntoRow(istrWorksheetName:=lstrWorksheetName,
istrStartingCell:=lstrStartingColRow,
istrArrayOfData:=mstrExcelRow) = False Then
Throw New Exception("Insert Error *************************")
End If