We have gotten reports from players that when a Boss Fight starts, the screen goes into 'Spotlight mode', but that the Boss himself may be outside of the screen's viewing area. Therefore, you cannot click on the Boss to attack them.
Today we wanted to share a workaround for this problem. When this occurs, you can use your computer's arrow keys to move the screen so that you can click on the Boss. This will let you fight them.
You can use the arrow keys to move the view around if you ever get stuck being unable to click upon anything in the game.
Hopefully this can get you back into the Boss Fights and allow you to pound on them. Now go get 'em!
--The Mafia Wars 2 Support team