rawaruska wrote: Problem not solved yet !!! CRITICAL !

When trying the debug mode I have this message juste before the reg form :

Warning: Cannot modify header information - headers already sent by (output started at /www/administrator/components/com_comprofiler/plugin.class.php:7271) in /www/administrator/components/com_comprofiler/library/cb/cb.session.php on line 74

Warning: Cannot modify header information - headers already sent by (output started at /www/administrator/components/com_comprofiler/plugin.class.php:7271) in /www/administrator/components/com_comprofiler/library/cb/cb.session.php on line 149

...

This means that something has outputed into the page source HTML and does not allow any HTML header to be sent anymore (e.g. cookies for sessions, or other important HTTP protocol elements).

As it worked before, maybe you can remember installing something else (e.g. joomla plugin or joomla plugin or language) or modifying something in joomla or language or extension, just before the issue started.

That can e.g. be a blank line or space after a closing "?>" tag or before an opening tag.

It would be worth cloning the site, then emptying on the clone the jos_cbsubs_subscriptions and jos_cbsubs_payment_baskets tables to avoid any expirations emails being sent, and try analyzing the origin of the problem by unpublishing one by one the extensions while there is no time pressure.