L4D2 Bad challenge

idk it supports L4D2, i just try use it and I got Bad challenge. Error

server console
```
RejectConnection: ip:port - Bad challenge.
```

client console
```
Connecting to ip:port | client port: port| Nick: leysourceengineclient | Pass:
Challenge: xxx|Auth: xxx|SKey: 320|VAC: 0
Connection refused! [challenge.
```