Javascript with VB help

Hi,

Just wondering if I can get some help, what I am trying to do is produce a popup window in asp using vb

My code:

 Sub ItemsGrid_Update(sender As Object, e As ImageClickEventArgs)
  
  
  if txtReplace.text = txtReplacedby.text then

  error_test()
  
  else

 'do some sql stuff

 end if

End Sub

 

Sub error_test()

imagebutton1.Attributes.Add("onclick", _
           "javascript:alert('Duplicate ID Identified, Please Correct.')")

End Sub

<tr><td><asp:ImageButton id="imagebutton1" runat="server"
  AlternateText="Save"
  ImageAlign="left" ImageUrl="http ...