I'm getting an Invalid Steam UserID Ticket, how do I fix this?
You are trying to connect to your own server.
If you have a server and a client behind the same router:
You will not be able to connect your client to your server from behind the router using the external IP address. You will not be able to connect to the Server by clicking on it in the full server browser window.
In fact, you will probably not be able to even see your Server in the ServerBrowser Window.
You must use the internal IP address.
What you do is go to:
Steam > Servers > Favorites then add your internal Server IP and port
For example: 192.168.1.100:27015 if this is what your Server says when you type in "Status" in the Server console.
Then always connect to your server from the favorites menu.
Two or more clients behind the same router
You might get this or an "expired" SteamID ticket if you are behind a router with other players and you are all trying to connect to the same server. Here is a detailed FAQ with information on how to fix this:
Log out and exit
If this is a problem for you on all servers then you can try fixing this problem by logging out of Steam and then logging back in again.
Check your Clock Settings
If this doesn't work then you need to check the date, time and year on your computer to make sure they are set properly. This should not be an issue with Steam itself, but it is a good idea to ensure it is set properly.
Two Computers, one Account Problem
Something else that can cause this is if there is another computer that is using the same Steam account.
When you log into a second computer with the same account that is running on the first, the Steam Ticket will invalidate on the first machine and transfer to the new Session.
This means that the first machine will then eventually prompt for a login to establish a new SteamUserID Ticket, and if the person on that machine logs in, then the ticket will then transfer back to him.
You need a unique Steam Account for each computer that is going to be online at the same time.
Stand-alone Server Uses a Steam Account
Stand-Alone Steam Dedicated Servers use a Steam Account, and if you are using the same Steam Account for your Stand-Alone Dedicated Server that you are using for your Client then this problem can occur as well.
Client Listen Servers and Client Dedicated Servers use the SteamID Ticket for the Client that they are run from so they don't have this problem.
Complex Computer networks might be configured in such a way that the Steam client gets NAT translated twice before it can get to the Server. NAT translation is the process where many computers can share one IP address.
Steam works very well with NAT, but will not work with double NAT, Steam must be able to verify the identity of the client and validate the SteamUserID Ticket and double NAT will prevent this from happening. There are no plans to modify Steam for this situation.
Another cause of this problem is if you are trying to connect to your own server and both the server and client are behind the same router.
In this case, you must connect to the server using the internal IP address and not the external IP address. An easy way to do this is to add the Server internal IP address and port to your client "Favorite Servers" and connect that way.
Dual WAN Networks and Routers
There are a few routers available that will accept two Internet connections and then manage the bandwidth so the client computers get better performance than just one connection. Unfortunately, since each WAN connection has a unique IP address, and client packets have a 50/50 chance of traveling through either path, this will also cause Invalid SteamUserID Tickets to happen.
If you are trying to connect to a local server where your LAN has two paths to the internet (two parallel NATs) and you are hosting a Server on one side, you can try to connect via the "external" IP instead of using the LAN IP. It might be best however to dedicate one WAN connection to just the Server and then have the other WAN dedicated for Clients. Clients would use the external (normal) Server IP then.
The bottom line is that one of these two things must be true:
a. The IP that the Game Server sees you connecting from is the same IP that the Steam network sees you connecting from, or
b. It must appear to Steam that your Client and the Game Server are using the same IP (you are both behind the same NAT).
If you are unable to meet these requirements then your network will be incompatible with Steam.
If this happens when you try to connect to a server, it might be because the Server or the Steam network is having problems. You need to try a different server or check on the Steam Status page and see what the current status is:
Normally, if this is a problem on your client (game) it will prompt you to renew your Ticket.