Squirrelmail webmail sudden login problem !?

[prisfeo]

ispconfig3 + Cento5.4, all works.

squirrelmail has worked perfectly till now.
now suddenly, when i access (with every configured accounts)
through the usual: http://myserver.example.com/webmail
i keep getting this error:
"Your session has expired, but will be resumed after logging in again."
and i cannot login..

i have cleaned browser cache, restart browser..always same problem..
i have not touch any code/files related to apache/squirrelmail
apache is on as normal.
(prior to reboot the server i have to understand if it can be a runtime problem)

what can be the problem ?

thanks in advance.

[till]

Take a look into the error.log of the website and the global apache error log.

[prisfeo]

hi Till..

i have retried to go to http://myserver.example.com/webmail
and tried to login..and after i have looked into:

/etc/httpd/logs/error_log
and
/etc/httpd/logs/access_log

in error_log: no logs about my navigation above,
so i think there are no errors.

in access_log there are these outputs:

mylocalip - - [02/Feb/2010:11:49:22 +0100] "GET /webmail HTTP/1.1" 301 337 "-" "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.1.4322; .NET CLR 2.0.50727)"
mylocalip - - [02/Feb/2010:11:49:22 +0100] "GET /webmail/ HTTP/1.1" 302 - "-" "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.1.4322; .NET CLR 2.0.50727)"
mylocalip - - [02/Feb/2010:11:49:23 +0100] "GET /webmail/src/login.php HTTP/1.1" 200 2168 "-" "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.1.4322; .NET CLR 2.0.50727)"
mylocalip - - [02/Feb/2010:11:49:23 +0100] "GET /webmail/images/sm_logo.png HTTP/1.1" 200 7396 "http://myserver.example.com/webmail/src/login.php" "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.1.4322; .NET CLR 2.0.50727)"
mylocalip - - [02/Feb/2010:11:50:09 +0100] "POST /webmail/src/redirect.php HTTP/1.1" 302 - "http://myserver.example.com/webmail/src/login.php" "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.1.4322; .NET CLR 2.0.50727)"
mylocalip - - [02/Feb/2010:11:50:09 +0100] "GET /webmail/src/webmail.php HTTP/1.1" 200 1269 "http://myserver.example.com/webmail/src/login.php" "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.1.4322; .NET CLR 2.0.50727)"

problem persist...

[prisfeo]

i decided to reboot the ispconfig server..
now webmail/squirrelmail works again..
bah..i'd like to know what was the problem..but most important
hope that will not pop out in the future..
...
...maybe it can be related to this file ?:

http://myserver.example.com/webmail/src/signout.php

i mean to session destroy functions..
or to this setting in php.ini:

; Initialize session on request startup.
session.auto_start = 0