Windows 7 and Windows 8 support UEFI (Unified Extensible Firmware Interface) implementations.
Symantec Encryption Desktop version 10.3.1 (formerly known as PGP Desktop) introduced support for systems running Microsoft Windows 8 64-bit in UEFI mode. Versions previous to 10.3.1 of Symantec Encryption Desktop do not support this configuration.
Refer to article TECH203071 for more details and requirements on UEFI support and Symantec Drive Encryption.