Solution
add to pproject global.asax
protected void Application_Error(object sender, EventArgs e)
{
//We save the error information to a file named Error.txt
StreamWriter sw = new StreamWriter(Server.MapPath("~/error.txt"), true);
sw.WriteLine(DateTime.Now.ToString());
//Server nesnesini GetLastError metodu sunucuda oluşan son hatayı Exception tipinden getirir. Bu da şu an oluşan hata olacaktır
if (Server.GetLastError().InnerException != null)
sw.WriteLine(Server.GetLastError().InnerException.Message);
else
sw.WriteLine(Server.GetLastError().Message);
//The Path property of the / Request object now returns the path information of the requested page
sw.Write(Request.RawUrl != null ? Request.RawUrl : "");
sw.WriteLine();
sw.Close();
Response.Redirect("Default.aspx");
}