Error CMS Page [PrestaShop\PrestaShop\Core\Domain\CmsPage\Exception\CannotEditCmsPageException codice 0]

[MarioB59]

Hello,

I'm using a 1.7.6.5 version of Prestashop for a new e-commerce shop. Everything was ok until yesterday when, as I tried to update the shop (it's stil on maintenance still it's not finished yet), 

I have an unexpected error [PrestaShop\PrestaShop\Core\Domain\CmsPage\Exception\CannotEditCmsPageException codice 0]

Moreover, when I go to other pages I have a 500 internal error everywhere, and I can't change or save nothing.

Can you help me please? I don't understand what happens

I don't have strange urls, accented urls...