When upgrading my MacBook Air to Mountain Lion I ran in to a problem, which drove me nuts for a few hours. After I started the install process of Mountain Lion the MacBook Air rebooted and presented me, as expected with a password screen for my File Vault 2 encrypted SSD. Since this is my first machine with an encrypted boot drive I already feared trouble with the encryption and I did not have to wait very long. I entered my password, which only caused the password field to shake as if it was rotten. My password is very long and it‘s not unusual I get it wrong the first time. After the fifth attempt I was convinced there was something wrong.
I rebooted the Air hoping it would boot back into Lion, which I did not. Even pressing the option key wouldn‘t help it. I thought it was broken but hesitated to enter the recovery key or go back to the backup I made with Carbon Copy Cloner.
Since the Air is only my second machine I set it aside and ignored the problem for a while. When I booted it up some hours later, my password still did not work but, much calmer now then befor, I discovered a small keyboard layout selection field in the top right corner. I switched over to a German keyboard layout and everything was fine again. (I‘m sorry that I have no picture of the screen)
Lessons learned. Apple isn‘t as perfect as I would love it to be. Passwords with special characters are tricky. Nothing new here but sometimes you have to experience it on your own.