Why this simple code gets this error ?

I get this error: "Conversion from string "test" to type 'Double' is not valid."
in this simple code I copied from web.
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Dim strFileShortName As String = "test" + DateTime.Now.Ticks & ".pdf" Dim strFileName As String = HttpContext.Current.Server.MapPath("reports\" & strFileShortName) End Sub Why it says I am trying to convert to double ? I did not tell it to convert...
Pls help, thanks