The panels in the server does not work

Hello everyone
(sorry in advance if my English is bad, I'm French)

For 1 month now, I have encountered a problem with the panels in a server. I have searched the internet many times but without success.

In my very first games on the "lifeboart" server in "survival mode". My panels were working.
As I said at the start, for 1 month almost impossible to communicate or write something on the panels. (See the pictures).

This problem also happened to a friend. Our signs worked at the start and overnight it didn't work anymore.
Yet the other players manage to write, but not us.

 
It's very embarrassing when a person waits for the answer on the panel and it says "Taccos!" or "i love my mom" or "2 + 2 = 4" ...
 
Anyone have the solution? Because I don't know what to do anymore.
Is it a permission problem? Or a parameter to modify?
 
Thank you for your reply