While we are working on the new update to fix still existing game launch issue please try the following workaround to have an ability play the game now:

Please go to this folder:
C:\Users\%USERNAME%\AppData\Roaming\Five-BN Games\LostLandsF2P

and delete this file: gameini.xml

Then the game should launch in a windowed mode. You also may try to switch to the fullscreen mode after that.

Please sorry for this problem. The update will be available soon.