I cannot select Multiplayer from the main menu in Duke Nukem Forever

You must be connected to Steam in order to use the multiplayer features of Duke Nukem Forever.

This problem can also occur if the Steam Community options are disabled for the game. To fix this:

1. Launch Steam, and go to the "Library"
2. Right click on Duke Nukem Forever and select properties
3. Be sure the "Enable Steam Community In-Game" checkbox is checked.