I had this problem with my logout script. I used the variable "lin" (logged in) to detect it.
For my login.php:
session_start();
session_register("un");
session_register("pw");
session_register("lin");
$un=$info["un"];
$pw=$info["pw"];
$lin=true;
For my logout.php:
session_register("lin");
$lin=false;
session_destroy();
For my header file:
session_register("lin");
if($lin){
session_register("un");
session_register("pw");
}
Hope this helps you 😃
EDIT: I made it a little more understandable.