Internal server error prestashop

Bonjour.

Nous sommes une boutique de vente virtuelle.
Sous Prestashop 1.7.6.5
J'ai déjà modifier le doc config et htaccess suite au tuto de prestashop mais toujours le même soucis.

Il arrive que certains ajouts (Pas tous) est impossible car nous avons le message :

Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator at [E-mail visible pour les membres Pro] to inform them of the time this error occurred, and the actions you performed just before this error.

More information about this error may be available in the server error log.

Additionally, a 500 Internal Server Error error was encountered while trying to use an ErrorDocument to handle the request.