Dear Philippe,
I was looking in to this for you and found that I have a similar error (see screenshot). I am running OpenREM on Windows. The error was because RabbitMQ was not running.
I have:
* removed the rabbitmq service
* opened a command prompt window
* navigated to the rabbitmq\sbin folder
* run the command "rabbitmq-server.bat"
* rabbitmq has successfully started
I then realised that celery was not running either, so I ran that in another command prompt window.
The server error has gone away.
I need to work out why the rabbitmq service wasn't working as it should have been.
I hope that helps in some way.
David