Error when trying to play Deathmatch off-line

[JFK]

I have just bought Episode 1 and also downloaded Deathmatch off Steam this time.

Now, it shows 100% ready on Steam and I can go into the game and create a server.

But while it says loading world it kicks me out of the game and gives the message "Unable to load authentication library. Exiting HL2 Deathmatch"

What am I doing wrong? Any ideas?

It's urgent, I am way behind on my beating quota...

 

[JFK]

Must maybe just add I can play HL2 and Episode 1 so my Steam account is working.

And of course I must ask if it can be played off-line. I only want to play it on LAN.

Thanks

 

[Xendance]

This happens to me when I'm using my brother's computer. Just start a dedicated server.

 

[JFK]

Looked around in the game and don't see an option in the menus to create dedicated server. Or should I use console,what command?

 

[Xendance]

Go to your tools tab on Steam and install Source Dedicated Server.

 

[JFK]

I installed Dedicated Server now. I can not LAN the game at the moment so the only way I can check if it works is by starting a dedicated server on my PC and then join that game and play against bots. Would that be possible somehow? Know it sounds a bit stupid trying to join your own server. No console commands or something like that?