track error on defaultRedirect?

I've added this in my web.config:

<customErrors mode="RemoteOnly" defaultRedirect="~/Site/Statics/Eroare.aspx">
          <error statusCode="404" redirect="~/Site/Index.aspx" />
        </customErrors>

Well, in Page_Load method o开发者_Go百科n Eroare.aspx page i try to print to my internal logs the error which caused this redirect but Server.GetLastError() is null...

Do you know why? Or any other solution to get the exception?

Thanks.

---

The key is to trigger the error in Global.asax file

    protected void Application_Error(object sender, EventArgs e)
{
    Exception objErr = Server.GetLastError().GetBaseException();
    string err =    "Error Caught in Application_Error event\n" +
            "Error in: " + Request.Url.ToString() +
            "\nError Message:" + objErr.Message.ToString() + 
            "\nStack Trace:" + objErr.StackTrace.ToString();
    EventLog.WriteEntry("Sample_WebApp",err,EventLogEntryType.Error);
    //Server.ClearError();
    //additional actions...
} 

More info: http://support.microsoft.com/kb/306355