Link Button Problem

Hi Dear all,
When I wrote following code in my code file for linkbutton,than on first click I can see that only Replaceimage.imageurl = "~/default.jpg" is fired while linkbutton1.PostBackUrl = "~/default.aspx"is fired on second click.
 
I want to change both things on first click.Thanks.
 
Protected Sub linkbutton1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles linkbutton1.Click
If Page.IsPostBack Then
AdRotator1.Visible = False
Replaceimage.Visible = True
Panel1.Visible = True
EniscopePanel.Visible = False
Replaceimage.imageurl = "~/default.jpg"
linkbutton1.PostBackUrl = "~/default.aspx"
End If
End Sub
...