Show Panel When Form Button Clicked

I Have a form, when the Submit button is clicked I want to reveal a Panel to show a message that says  "Sending Form...".  I am unable to get the panel to show when the form button is clicked.  Here is my code.
CODE BEHIND:
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load 'Hide progress Panel on pageLoad progressPanel.Visible = False End Sub Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click 'Show panel while form sends progressPanel.Visible = True Dim dater As String = Now.ToString() If txtAttachment.PostedFile IsNot Nothing Then Dim intFileSize As Integer = txtAttachment.PostedFile.ContentLength ' The file size limit If intFileSize > 3145728 Then Label6.Text = "File is so l ...