Schau mal wo in der php.ini der Standardpfad für die Session liegt. Vielleicht hat der Webserver keine Zugriffsrechte und kann die Session nicht schreiben.
Ansonst kannst du in php des Sessionhandler überschreiben und den Pfad an eine andere Stelle verlegen.
Session Support enabled
Registered save handlers files user sqlite
Registered serializer handlers php php_binary wddx
Directive Local Value Master Value
session.auto_start Off Off
session.bug_compat_42 On On
session.bug_compat_warn On On
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 100 100
session.gc_maxlifetime 1440 1440
session.gc_probability 1 1
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 \xampp\tmp \xampp\tmp
session.serialize_handler php php
session.use_cookies On On
session.use_only_cookies Off Off
session.use_trans_sid 0 0
Nichts verdächtiges aus der error.log
[Mon Nov 30 17:30:58 2009] [notice] Digest: generating secret for digest authentication ...
[Mon Nov 30 17:30:58 2009] [notice] Digest: done
[Mon Nov 30 17:30:59 2009] [notice] Apache/2.2.12 (Win32) DAV/2 mod_ssl/2.2.12 OpenSSL/0.9.8k mod_autoindex_color PHP/5.3.0 mod_perl/2.0.4 Perl/v5.10.0 configured -- resuming normal operations
[Mon Nov 30 17:30:59 2009] [notice] Server built: Jul 22 2009 11:35:54
[Mon Nov 30 17:30:59 2009] [notice] Parent: Created child process 5828
[Mon Nov 30 17:31:00 2009] [notice] Digest: generating secret for digest authentication ...
[Mon Nov 30 17:31:00 2009] [notice] Digest: done
[Mon Nov 30 17:31:01 2009] [notice] Child 5828: Child process is running
[Mon Nov 30 17:31:01 2009] [notice] Child 5828: Acquired the start mutex.
[Mon Nov 30 17:31:01 2009] [notice] Child 5828: Starting 150 worker threads.
[Mon Nov 30 17:31:01 2009] [notice] Child 5828: Starting thread to listen on port 443.
[Mon Nov 30 17:31:01 2009] [notice] Child 5828: Starting thread to listen on port 443.
[Mon Nov 30 17:31:01 2009] [notice] Child 5828: Starting thread to listen on port 80.
[Mon Nov 30 17:31:01 2009] [notice] Child 5828: Starting thread to listen on port 80.
Auszug aus meinem Server (wo alles läuft, alles gleich)
session
Session Support enabled
Registered save handlers files user
Registered serializer handlers php php_binary wddx
Directive Local Value Master Value
session.auto_start Off Off
session.bug_compat_42 On On
session.bug_compat_warn On On
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 100 100
session.gc_maxlifetime 1440 1440
session.gc_probability 0 0
session.hash_bits_per_character 4 4
session.hash_function 0 0
session.name PHPSESSID PHPSESSID
session.referer_check no value no value
session.save_handler files files
session.save_path /var/lib/php5 /var/lib/php5
session.serialize_handler php php
session.use_cookies On On
session.use_only_cookies Off Off
session.use_trans_sid 0 0
Sag mal du hast nicht zufällig windows vista und hast den xampp ins Default Verzeichnis installiert oder? Wenn ja wird das nicht funktionieren, da er nicht im "Programme" Verzeichnis von Vista schreiben kann.
Aufgrund fehlender Schreibrechte der Vista Standardinstallation für das Verzeichnis "C:\Program Files" ("C:\Programme"), empfehlen wir XAMPP in einem alternativen Verzeichnis ("C:\xampp" oder "C:\meinverzeichnis\xampp") zu installieren. "