My Mid-2012 Mac Book Air running an up-to-date install of Mountain Lion crashed the other evening (browsing the web, one tab started beach-balling, and refused to be force-quit so I forced a restart).
When restarting, it seems to accept my user's password to unlock the FileVault 2 encryption (I'm certain the password is correct, and typing a known incorrect password results in a shaky input field). The next screen is a grey screen, with a spinning progress wheel. Eventually a grey embossed sign is displayed, and that's about as far as it progresses. Booting using verbose mode (⌘+V) results in repeated lines of
Still waiting for root device being logged.
Entering recovery mode (⌘+R) to try and restore from a TimeMachine backup, or zap the drive and re-install from the internet gets me as far as a password input box requesting I "Enter a password to unlock the disk Macintosh HD", but I cannot get past this screen despite entering correct passwords for both users who have the ability to unencrypt the drive (And I think getting past the initial unlock screen with these passwords demonstrates that they work, but I'm happy to be corrected), with the password box just shaking and rejecting the password.
Attempting to unlock the drive from the Terminal in Recovery Mode fails to mount the drive, but claims to have been unable to unencrypt it:
-bash-3.2# diskutil cs unlockVolume XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX Passphrase: Started CoreStorage operation Logical Volume successfully unlocked Logical Volume successfully attached as disk13 Error: -69842: Couldn't mount disk
I've run the hardware tests, and they showed no problems. I've seen this question describing similar symptoms, but that solution did not appear to help, with the password field of the Unlock Drive menu option in Recovery Mode's Disk Utility also rejecting the password.
Essentially my question is "how can I get my laptop back into a working state"? I have recent TimeMachine backups, and so if the least painful is to format the drive and start again then I'm happy to do that, but at present I can't manage to get the drive wiped.
I have my FileVault Encryption key if necessary.