ERROR 500 after upgrading from 1.11 to 1.11.1 (2 replies)

Hello everyone, I'm using Piwik since a year and today I expected my first critical problem.

I started the automatic update from 1.11 to 1.11.1 version and, at the end of the installation, the page refreshed but gave me a 500 error. I can't access to any of the sections anymore, the same for the login page!

How can I fix this?

Thanks