Hi Mr Papa and -Radio-,

Thanks a lot for your help. Since I didn't manage to solve my problem otherly, I decided to move my Wordpress website on a dedicated server. Same plugins activated, same code, etc. but different php.ini settings on the Apache server (cf. /etc/php5/apache/php.ini, given that I run PHP5 and Apache 1.3) : the result ? No more 500 error !

That's why I think this problem can happen when mutualised web hostings don't allow sufficient memory to their users, or when php.ini settings (the “memory_limit” parameter) are not correctly set.

I hope this can help others.

Best regards and thanks for the amazing job,

Augustin