Hi,

 I would like to show alert message once return value is clear then it only will redirect to GameListing.aspx page, but there is no alert mesage out at all. any idea? thank you  

Code in aspx.vb

If (return_value = "clear") Then               
         ClientScript.RegisterClientScriptBlock(Page.GetType, "Script", "<script language='javascript'>alert('Please follow up data in form');</script>")
          Response.Redirect("GameListing.aspx?product_id=" + Request.QueryString("product_id"))
End If

Two issues: first of all, you need to use RegisterStartupScript (instead of RegisterClientScriptBlock) for the alert to show "automatically".  But the bigger issue, is that in the code behind you redirect to a different page, so the alert will never show.  Maybe change your code to include a window.location=blahblah, after the code for the alert.  Which means that after the user clicks OK, the page gets redirected to GameListings.aspx.  Something like that...

Try to use following:

 Dim scriptStr As New System.Text.StringBuilder
        scriptStr.Append("<script language='javascript'>alert('Please follow up data in form');")
        scriptStr.Append("window.location='"GameListing.aspx?product_id=" + Request.QueryString("product_id")'; </script>")
        If Not Page.ClientScript.IsStartupScriptRegistered("PopupScriptWithLoc") Then
            Me.ClientScript.RegisterStartupScript(Me.GetType(), "PopupScriptWithLoc", scriptStr.ToString(), False)
        End If