Invalid steam userid ticket fixAugust 31st, 2012 by Brentonator It has recently come to our attention that an epidemic is sweeping the Source mod community. Players all across the globe are encountering this error when trying to play their favorite games:
For those of you experiencing this issue, fear not! There may be a solution.
- Shut down steam.
- Delete the "config" folder in your Steam directory.
- Open Steam again
- Steam will redownload all of the files you deleted and verify the contents of your steamapps folder. (Credible sources say this process only takes a couple minutes)
- Test the game!
Thanks, Paladin for this answer.
Please see this Steam Support page for more troubleshooting options: