I receive the error: 'You have been disconnected from the server. Reason: Error verifying STEAM UserID ticket' when I try to connect to a server.
If the Steam Network is down or too busy you may not be able to connect to a Game Server - to determine whether or not this may be the issue, please check the Steam Status Page - if the last update for that page is more than 20 or 30 minutes behind, there may be a Steam network outage.
Please check to see if there are other players having the same problem on the SteamPowered Forums.
If it does appear as though the Steam network is down, you must wait until the problem is resolved.
If you continue to receive this error message, the issue can most likely be resolved by restarting the Steam client.
If restarting Steam does not resolve the issue, please exit Steam and delete the following files from your Steam directory:
The files should be found at C:\Program Files\Steam\ (the location on your machine will vary if you specified a different installation folder, or if you have moved your Steam installation).
If you continue to see this issue, please contact Steam Support: