There is this from the 10.1.2 release notes:
Resolved an issue that prevented users from accessing the PGP BootGuard screen to authenticate Windows
systems. [28338]
http://www.symantec.com/business/support/resources/sites/BUSINESS/content/live/DOCUMENTATION/3000/DOC3583/en_US/pgpDesktopWin_1012_releasenotes_en.pdf
But there is also the "Sandy Bridge issue" where newer i5 and i7 intel processors were not compatible with Bootguard. This was not fixed until 10.1.2 Build 50 - service pack 3 (which you have to request from support) and also subsequently 10.2.0.
http://www.symantec.com/docs/TECH160346
I would recommend, after decrypting, to upgrade your PGP desktop version and backup your files and then try encryption again.