Out of no where my php sessions does not work anymore. The server have been running fine for several months.

I'am running Ubuntu 11.10 (GNU/Linux 3.0.0-14-server x86_64) with nginx/1.0.11 and php 5.3.19-1~dotdeb.0

Session info copied from phpinfo()

Session Support enabled
Registered save handlers    files user memcached
Registered serializer handlers  php php_binary wddx

Directive   Local Value Master Value
session.auto_start  Off Off
session.bug_compat_42   Off Off
session.bug_compat_warn Off Off
session.cache_expire    180 180
session.cache_limiter   nocache nocache
session.cookie_domain   no value    no value
session.cookie_httponly Off Off
session.cookie_lifetime 0   0
session.cookie_path /   /
session.cookie_secure   Off Off
session.entropy_file    no value    no value
session.entropy_length  0   0
session.gc_divisor  1000    1000
session.gc_maxlifetime  1440    1440
session.gc_probability  0   0
session.hash_bits_per_character 5   5
session.hash_function   0   0
session.name    PHPSESSID   PHPSESSID
session.referer_check   no value    no value
session.save_handler    files   files
session.save_path   /tmp    /tmp
session.serialize_handler   php php
session.use_cookies On  On
session.use_only_cookies    On  On
session.use_trans_sid   0   0

I have setup the following php script to test with:

error_reporting(E_ALL); 
ini_set('display_errors', true);

error_log($_SERVER['REMOTE_ADDR'] . ' visited test page');

if(session_start())
    echo "Session started <br />";
else 
    echo "Session failed <br />";

echo '<a href="?', time(), '">refresh</a>', "\n";

echo '<pre>';
echo 'session id: ', session_id(), "\n";

$sessionfile = ini_get('session.save_path') . '/' . 'sess_'.session_id();
echo 'session file: ', $sessionfile, ' ';
if ( file_exists($sessionfile) ) { 
        echo 'size: ', filesize($sessionfile), "\n";
            echo '# ', file_get_contents($sessionfile), ' #';
}
else {
        echo ' does not exist';
}

echo PHP_EOL;

$_SESSION['number'] = (int) @$_SESSION['number'] + 1;

var_dump($_SESSION);
echo "</pre>\n";

session_write_close();
echo 'done.';

It tells me that the session file exists, but my session id changes on each refresh..

What is going wrong? There is no output to any error logs at all.. :/

Please help!