i tried playing zombie panic source  and when i join a server it says invalid steam user id ticket  i tried logging off and on but it still does not work i never knew this was still a problem
any help thanks:)
 
and yes i have tried using Google for help .

CAPS! 

annd no idea. does it do that for joining any server or just that specific one on zombie panic source?

I had that problem with Left 4 Dead 2 once when I installed the add-on support. Then I deleted it then it worked again. Don't know if that will make it work for your game.

try reinstalling it would be my best guess. that usually helps no matter the issue.