TOPIC: ?

If you go to Options>Other>Allow all content

I'm not sure if this would help but It might.
The only other thing I can suggest is googling it!

Garry's mod has had an update.
Chute will have to update the server, this might take a while then you are able to join again!

This accounts for each player who has updated their game and for each Zarp server.
It happens more often, so just be patient and you'll be able to play again once Chute is to update the server.