Hello.  Please pardon my English.  My French is very poor.

I thought this might be of some assistance.  I upgraded Piwigo and immediately had a similar problem -- the Admin page returned only a blank page and the "Class 'DateTime'" error -- until I figured out my mistake.

My Piwigo setup had been running fine with PHP 5.3.  In order to get VirtualMin (WebMin) to install properly I recently downgraded to PHP 5.1 on my Centos 5.10 VPS.

I know Piwigo requires PHP 5.2 or higher.  (However I did notice that everything including the Admin page seemed to load fine on PHP 5.1, until I made this new Piwigo upgrade.)

So I then installed the "PHP53u" modules based on recommendations like those at serverfault.com/questions/111458/upgrade-centos-5-tot-php-5-2-or-5-3-recommended-way

The "yum replace" technique is very helpful.

But no matter what I did, the Admin page still wouldn't load and still returned that Class DateTime error.  I was able to literally comment out that section with /* */ in the functions.inc.php file, and then the Admin page WOULD load.  But obviously that was a bad, temporary solution.

Finally I realized that it didn't matter what version of PHP I had installed -- Piwigo still thought I was at PHP 5.1.  I noticed this by monitoring "admin.php?action=phpinfo", a page that WOULD always load properly.

So the simple SOLUTION for me was that I had to restart Apache!  (For me, "service httpd restart".)  Then the php-cgi picks up the newly installed PHP 5.3u, and everything was fine.  The new Piwigo Admin page loads normally.

It was a very "newbie" mistake on my part, but I thought perhaps others would have a similar problem.

Bon chance.

Bonjour,

J'ai également ce problème avec DateTime et Free.
J'ai mis le code proposé par Blaudez.

Il n'y a pas moyen de le modifier pour que les dates des photos s'affichent correctement?
Perso je ne m'y connait pas du tout en PHP...

Merci

j'ai le même problème...comme je viens de passer chez orange, je suis mal parti ! quel hébergeur gratuit me conseillez-vous ?
merci

c'est vrai que l'investissement est quand même modique. merci pour la réponse.