Symfony 2 "Your session has timed out or you have disabled cookies"

I ultimately found the answer here: Symfony authentication - can't get past login page in production (The answer by pleerock)

But wanted to link the error message in my subject line with this solution below:

security:
    firewalls:
        main:
            form_login:
                require_previous_session: false

This fixed the issue for browsers which hadn't been logged in prior to the problem.

For my browser which had already been logged in, I had to manually delete the session cookie to get things working again.