Since updating to Parallels 12, the ALT key no longer works. I'm running is full screen mode. ALT-TAB to switch between open apps doesn't work. Application shortcuts don't work. It seems that any functionality in any application involving the ALT key does not work properly, invoking some another command instead when pressed. I've reinstalled Parallels Tools and "Send OS X system Shortcuts" is set to auto.
Select Parallels icon (II) from Mac tray > Preferences > Shortcuts > Applications Shortcuts > Scroll down and disable "Show Next and Previous Tab" keyboard shortcut. Choose Keyboard setting between "Don't Optimize for games" "Optimize for games" click here for steps.
