add rich:messages to the page.
Good morning Ilya :)
The page already contains a rich:message and nothing is being displayed.
What I noticed is that there is ajax request sent by the autocomplete indeed I have a popup panel which displays a loading popup on ajax requests. So, I see this modal when I use the autocomplete but nothing is happening !
Allright, I found the answer, the <a4j:region> had to be placed INSIDE the <rich:collapsiblePanel>.
I guess because the collapsiblePanel is in ajax mode, I had to include the region inside.