Lobby Map Error
From Obsidian Conflict Wiki
Lobby maps are maps which allow you to choose a playable map or campaign. They end in "_lobby".
Many times you will choose a map in a lobby and the screen will fade to black, hang, then snap back to full brightness again. In this case, the server you are on is not set up properly and you should try joining a different server.
Suggestion: Keyfox servers are run by developers of Obsidian Conflict and are up to date and reliable.