[SM-USERS] Blank login page: Failed to initialize session module

[<squ...@cl...>]

Hello,

I'm running SquirrelMail 1.4.3a on an hardened Linux with PHP 4.2.3 on 
Apache 1.3.27.
I made no change to my Apache or PHP configuration recently, and 
everything was working well for about one year.

Since yesterday, no user can log into SquirrelMail. The login.php 
returns nothing but a blank page. I can still access other PHP scripts 
on the server and access my mail by using an imap client. I restarted 
httpd and imapd just to be sure. No change. I tried to update to 1.4.4. 
No change. I searched the archives and google but found nothing usefull 
for me.

Here is what I get in my php_error.log:

PHP Fatal error: Failed to initialize session module in 
/home/httpd/ssl.xxxxx.net-443/html/webmail/functions/global.php on line 
295
PHP Warning: Failed to write session data (user). Please verify that 
the current setting of session.save_path is correct (/var/run/php) in 
Unknown on line 0

Installed plugins:

$plugins[0] = 'mail_fetch';
$plugins[1] = 'newmail';
$plugins[2] = 'message_details';
$plugins[3] = 'filters';
$plugins[4] = 'metea';
$plugins[5] = 'vkeyboard';
$plugins[6] = 'calendar';
$plugins[7] = 'folder_sizes';
$plugins[8] = 'user_special_mailboxes';
$plugins[9] = 'abook_take';
$plugins[10] = 'folder_synch';
$plugins[11] = 'gpg';
$plugins[12] = 'show_user_and_ip';
$plugins[13] = 'timeout_user';
$plugins[14] = 'image_verification';
$plugins[15] = 'pupdate';
$plugins[16] = 'delete_move_next';
$plugins[17] = 'xheader';
$plugins[18] = 'view_as_html';

I really don't understand and it's driving me crazy... Any hint?

Regards,

Pierre