Thank you for your help.
This is what happens:
We have 2 versions of our website, english and french. When I'm logged in, I'm on the english version by default. If I need to edit a page, I click "edit page" on the cornerstone section and it is working.
When I switch the language for french, and I would like to edit the page, I get the conflict message. For every pages, not only my homepage.
Something that is also really weird is that, I'm the only person who gets this problem internally. My other coworkers can access this step.
My developer is not in this week, do you think you can help me if I give you my logins informations ? Otherwise I will wait for his return.
(dont't know if this screenshot can help...)