Can only access BO with debug mode on (1.7.6.3, no error code)

[DShiller]

Hi,

A client is running PS 1.7.6.3 on their website. Everything worked well but suddenly today they emailed me saying they couldn't access the back office any more.

On Firefox accessing the admin page gives me a blank page. But if I turn debug mode on in the config file, I can access it just fine. Chrome gives me their default HTTP error 500 page (which is different from the Prestashop error 500 page).

It did give me the attached warning when logging in, which is new to me (last time I logged into that site was a month ago), but I could still use the back office fine -- but again only if I turn on debug mode. Regarding that warning, I originally assumed this was causing the bug, and so I added an else{} statement in the file, as outlined here: https://github.com/PrestaShop/PrestaShop/issues/10934#issuecomment-492455546.

This did remove the pop-up warning, but the bug is still there.

[idnovate.com]

This is a notice, not an error, so it's not causing an error 500.

Check logs to get the real error.