I tested OVH fix for the previous versions of Piwik, it resolved my problem.
But I updated to the 1.8.4 version of Piwik, and I cannot apply the OVH fix anymore, as the files does not exit anymore.
Is there a way to make 1.8.4 work at OVH ? (it freezes at startup, and only one or two widget can load…the other can’t.)