If you made the map, it probably suffers from the Wrong Map Version bug.
Workarounds:
1) Find the last map that the server played which had at least 3 sceneries used, load the map in singleplayer, and then return to menu and connect to the server.
2) If your map is the first map to be used, quit your soldat client completely, and connect directly to the server upon re-launching.
Fix for the map:
Ensure the map has at least 3 sceneries used (actual files, not in-game images).
If you still have problems, you should try to rename/delete the map from your local soldat, and let the server send it to you when you connect.
