Possible work around for windows 7 users: run Civ V, Civ V Launcher, Mod Buddy, World Buillder in compatbility mod for xp sp3.
I haven't tested it out myself, but somebody on the steam fourms says it works.
EDIT: Other possible solutions:
* Start World Builder -> It is blocked on Loading screen
* Open a Command Prompt (Windows 7: Windows Menu -> cmd.exe)
* Type cd C:\Program Files(x86)\Steam
* Type steam.exe -applaunch 8930 \dx9 -Nexus 4320
* After few seconds/minutes World Builder will unfreeze
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1 launch windows task manager (keyboard azerty -> ctrl+alt+del)
2 exit steam
3 launch SDK world builder via the exe in the steamapps civ 5 SDK folder
4 it and steam should load
EDIT 2: The last one seems to work for a lot of people. You can view the thread here: http://steamcommunity.com/app/8930/discussions/0/882966056463177513/#p3
EDIT 3: I can confirm the last method works for me. Windows 7.
Now, can anybody tell me how I am supposed to make one of those mega huge maps like the earth ones? Isn't the limit in the worldbuilder smaller than that?
This did not work.
This did just open your map from your MODS. Right click, open with worldbuilder.World Builder Editor tool or just load the mod through the mod loader menu.
1. Go here C:\Users\Administrator\Documents\My Games\Sid Meier's Civilization 5\MODS\WWII European Theatre (v 2)
2. Right Click on your map (In my case, WWII European Theatre (v 2)). Where it says open with, select Civilization V World Builder. You can do this then you may have to restart your system to get it to work a second time.
Meh! I got it to open a few times messing around. Now it won't open again. At least I found out what difficulty to set the AI handicap too.