One more login problem

What suddenly started to happen is that noboby can login. All users are recognized, listed as logged and trated as if they were another user (see enclosed picture). You can login again as many times as you want, and you'll get listed as many times as you tried (as if it were different users) but never treated as an authenticated user.

This has been coincident with the opening of a top domain. The site was originally developed as eng.i-iter.org, and had a default dir pointing to a duplicate of it, so it could accessed as i-iter.org, too. Now the default directory is gone and an indipendent i-iter.org install as appeared. This higher level domain works with no problems.

I verified that what described at http://drupal.org/node/61900 (comment 23) is not my problem by running the associated script, and also tried changing my settings.php to

/**
 * PHP settings:
 *
 * To see what PHP settings are possible, including whether they can
 * be set at runtime (ie., when ini_set() occurs), read the PHP
 * documentation at http://www.php.net/manual/en/ini.php#ini.list
 * and take a look at the .htaccess file to see which non-runtime
 * settings are used there. Settings defined here should not be
 * duplicated there so as to avoid conflict issues.
 */
ini_set('arg_separator.output',     '&');
ini_set('magic_quotes_runtime',     0);
ini_set('magic_quotes_sybase',      0);
ini_set('session.cache_expire',     200000);
ini_set('session.cache_limiter',    'none');
ini_set('session.cookie_lifetime',  2000000);
ini_set('session.gc_maxlifetime',   200000);
ini_set('session.save_handler',     'user');
ini_set('session.use_only_cookies', 1);
ini_set('session.use_trans_sid',    0);
ini_set('url_rewriter.tags',        '');

/**
 * We try to set the correct cookie domain. If you are experiencing problems
 * try commenting out the code below or specifying the cookie domain by hand.
 */
ini_set('session.cookie_domain','eng.i-iter.org');
ini_set('session.auto_start', 0);

No changes. I'm thinking that this must be some sort of loss of session data, but have no clue at how I should direct my assistance service, because my local install does not have any such problem.