The error happens on our National server as well. I've filed a support ticket there as well. The problem is simple... you have 150% attack and you attack a player with 400%. You press autobattle, and you wont see a result button. You need to refresh the game or watch for hours how a 150% attacker defeats 400% defence. (The browser become very slow, and may even crash)
Never the less, once the started again you can continue the battle. and finish it by hand or auto.
NOTE: When someone has 700% defence, you need to restart your game 4 TIMES before in ordet to get back to your city.
I believe there is someting serious wrong with defence properties, and the system cant calculate that far ahead - it takes well over 200 shots to defeat 400%... Try attacking me at Beta with 150% to reproduce the error.