Thanks Jade.
In ACS Service contracts I've uninstalled:
Contract Implementation Label Owner
=======================================
FtsContentProvider :: forums_message :: forums_message :: forums :: Install
And the precedent error message doesen't show anymore in error.log.
I have a new one though :) =>
Warning: template::form::check_elements: MISSING FORMWIDGET: search:search:formbutton:ok
but it doesn't seems too serious.
cheers.
Yves.