its simple change in the game to fullscreen to window ,close the game open it and change it again to fullscreen

Thanks, but thats temporary not permanent. If you Alt+Tab while in game to see your desktop and do something (like load up FRAPS) it will revert back to the black bars and you will have to do what you instructed all over again. Crytek please patch a permanent fix on this issue. ANNOYING.

Alt+Enter will toggle full screen/window in almost everything that supports full screen.

But yeh it is an annoying mistake.