Filevault 2 is a new OS X 10.7 Lion feature that secures your data, should your Mac get stolen. It does so by not only encrypt your home folder like the predecessor, but your entire hard drive (or partition). That means in order to read the Lion volume, you have to unlock it first. This happens automatically when you boot from Lion installation, where you almost immediately get presented with a login screen, before the system even boots.

Obviously this doesn’t happen when you boot to your Boot Camp Windows volume. And that becomes a problem when Boot Camp 3.2 tries to mount your Lion partition. Since the volume is encrypted, and therefore unreadable, this will result in a nasty error which throws you a blue screen of death (BSOD).

If you, like me, made the mistake of enabling Filevault 2 before updating the Boot Camp support software to version 4.0 on your Windows installation, there is a solution. Instead of disabling Filevault 2, update the Boot Camp support software, to just re-enable Filevault 2, you can prevent Boot Camp from trying to mount the Lion volume. This saves a lot of time encrypting your drive.

To do this you have to follow a couple of easy steps:

  • Boot into Windows Safe Mode
  • Go to C:Windows\System32\Drivers
  • Rename AppleHFS.sys and AppleMNT.sys to AppleHFS.sys.old and AppleMNT.sys.old
  • Reboot

Boot Camp 3.2 will no longer try to mount your Lion volume and get the error, but you will not be able to browse you Lion volume from Windows. After this you can just update to Boot Camp 4.0 if you wish to do so.