Currently there is problem on the steam side which prevents the game clients from getting an authorization. It's a common problem for several games including ours.
I wrote several messages to the steam support but they didn't respond yet.
Sorry for the inconvenience, I will update this post as soon as I can get any further info.
UPD. Should work now.
UPD2. 10 feb - The same problem again.
UPD3. Works again.
UPD4. 11 feb - This time steam gives internal error (that's why you can see a message in the game).
UPD5. 11 feb - I'm turning the server off, to save livestock.
UPD6. Valve said they found and fixed the issue. Server is up.