If you see this message, first of all you need to make sure that the server of King's Bounty: Legions is not undergoing the routine maintenance (you can always find the information regarding the maintenance schedule on our website, forum and Facebook page).
If there's no maintenance taking place and you're not able to enter the game, we'd recommend you to clear your browser's cache and the cache of Unity Player. If this won't help, try to reinstall the Unity Player and your browser as well (make sure you're using the latest version).
For now, the game does not support 64-bit browsers.
If the given recommendations did not help you at all, you can always submit a ticket to our Support Service.