TF2 singleplayer not possible in offline mode

[Proletheus]

When I start a singleplayer botmatch or training in Steam offline mode, there's usually an error message after about 1minute saying that a connection to the VAC servers could not be made. This makes the game unplayable without internet connection for me. I run Xubuntu 12.10 with native Steam for Linux.

[Proletheus]

Now it works, thank you!