’Too many redirects’ error after upgrade

I’m upgrading a SPIP site from v1.8.1 to v2.1.1 (latest stable version). Everything went fine : I can browse my upgraded site locally without problems.

However, when I go to /ecrire and log in, I get a ’Too many redirect’ error, both in Chrome & Firefox. Clearing cookies doesn’t help : each time I log in, the error comes up.

There are no redirects set up in my Apache virtual host.

Does anyone what may be causing this error ?

Thanks.