Google-chrome – Why would Chrome/IE not persist cookies but Firefox works just fine

A 500 Internal Server Error indicates that Chrome does try to load the page and even gets a server response (being the 500 error). So, the server fails. It probably has some logs?

As cookies are stored per (sub-)domain, and localhost and 127.0.0.1 are different domains, my bet is that Chrome has an old cookie for localhost, which has not yet expired, but is somehow no longer valid.

Even if PHP and phpMyAdmin are backwards compatible (so would handle differences after upgrades), the troublesome cookie might have been created while you were testing the new PHP and new phpMyAdmin. And now that you reverted the upgrade either PHP or myPhpAdmin does not understand the newer format of the cookie or a session it refers to.

• For sessions, a browser's session cookie holds an id which on the server refers to "serialized" PHP objects. So, maybe the serialization format has changed in newer versions of PHP, and the old PHP does not know how to handle the newer format.

• For other cookies, maybe phpMyAdmin has stored serialized objects in the cookie directly, or in its database, or simply expects different data than it finds in the cookie.

To test the above:

1. To see if a session cookie is the culprit: restart Chrome and try again.

2. To see if a regular cookie is causing this without wiping it yet: try an incognito session, which does not send existing cookies to the server. If that works: clear the localhost cookies.

If this does not work, then you need to find the 500 error in the server's log.