At what point did this happen? When you turn on FV it reboots and starts the encryption... did that happen and did the encryption complete.
Try a command-r boot to recovery and see if the disk is visible from there in Disk Utility?
I enabled FV and when I (later) went to reboot, it wouldn't. I have tried booting from the recovery disk and when I select the disk (it is visible in Disk Utility) and click file/decrypt, it looks like it is starting but the progress window says there is an error.
Frustrated.
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While booted on an external drive, I go into DiskUtil and right click on the mac drive and select "unlock". It is now mounted.
What can I do now to decrypt it so I can boot from that drive?