Unwanted logout on adding stuff to database

I am using the PHP Login System and I am very happy with it but I have a great/small problem:
Sometimes when adding things to the database like a insert, or deleting or editing it gives me a logout from the system.
I have created a second user group besides admin, but I don't know if it has anything to do with it.
I think that with the admin session I never get log out, but with another type of user I always get it...

I have a menu part which is where I am checking the session with this code:

Code:

<?
include("include/session.php");
?>
<?
/* User is not logged in */
if(!$session->logged_in){
?>
<meta http-equiv="refresh" content="0;url=naoautorizado.php"/>
<?
}
/* User is logged in */
else{
?>

And every page which I am using calls that menu like a include.

Can you help me please?