Code:
header("Cache-Control: no-cache, no-store, must-revalidate");
HTTP 1.1. header("Pragma: no-cache");
HTTP 1.0. header("Expires: 0"); // Proxies.
add this to your admin/incudes/header.php or menu.php and clear the browser cache.
I found out that new browsers are messing with login cookies on older scripts. If mojo haven't changed anything on server then this should fix it.