A small update was rolled out a bit ago for the Left 4 Dead dedicated servers. Undoubtedly, this will be the first of a handful of updates to come.
A small fix for the Linux and Win32 L4D Demo Dedicated Servers have been released. Please run hldsupdatetool (with either the game parameter of l4d_demo, or left4dead) to get the new files. This should allow dedicated servers to run.Again, admins should run hldsupdatetool to get the update. There are still issues being reported of servers coming up as LAN only, so expect another update soon.