Sessions get messed up on external host

The problem sounds like this: The log-in using sessions works perfect on my localhost, but when the EXACTLY same files are uploaded to my host (hostgator), the sessions don't or, or they get messed up. Also the log-out feature doesn't work on the host.

I've checked and every page has the session_start(); inside it.

The session is not destroyed, even if my logout.php looks like this:

<?php
session_start(); 
$_SESSION = array();
session_unset();
session_destroy();
header("location:index.php");
exit();
?>

Any suggestions?

I noticed on Firefox with Firebug that your pages are all cached . Your session is working fine, but your page are cached, making login and logout quite (messed up).

Disable HTTP caching for your dynamic pages.

See Firebug output:

Response Headers

HTTP/1.1 304 Not Modified
Date: Thu, 14 Oct 2010 13:16:50 GMT
Server: Apache mod_fcgid/2.3.5 mod_auth_passthrough/2.1 mod_bwlimited/1.4 FrontPage/5.0.2.2635
Connection: Keep-Alive
Keep-Alive: timeout=5, max=100
Expires: Thu, 14 Oct 2010 16:16:50 GMT
Cache-Control: public, max-age=10800

Request Headers

GET / HTTP/1.1
Host: www.piataterenuri.info
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2.10) Gecko/20100914 Firefox/3.6.10
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 115
Connection: keep-alive
Cookie: PHPSESSID=55aea3f792334052dc673f85feb0b54a
If-Modified-Since: Wed, 13 Oct 2010 13:47:53 GMT
Cache-Control: max-age=0

PHP manual has already an example on how to disable caching:

http://php.net/manual/en/function.header.php

<?php

header("Cache-Control: no-cache, must-revalidate"); 
header("Expires: Sat, 26 Jul 1997 05:00:00 GMT"); // Date in the past

?>