Once a system has been encrypted with PGP Whole Disk Encryption, in order to boot the system, the passphrase must first be authenticated.
Once the PGP BootGuard screen comes up, and enter the passphrase. As soon as the enter key is pressed, hold down the option key and s at the same time.
This action must be done immediately after enter. If not, the system will reboot normally and another attempt must be made.