Via darknet :

For the past day or so I’ve been seeing endless people tweeting about how the latest Mac OS X update b0rks your Mac if you are using PGP full disc encryption. It’s a pretty nasty bug, but thankfully it can be recovered from fairly easily.
If you are just looking for a quick solution, you can:
a) Not apply the update (as recommended by PGP)
b) Decypt your volumes, apply the update, then re-encryp_

For the LOL:

Users of PGP’s Whole Disk Encryption for Macs got a nasty surprise when they upgraded to the latest OS X update once they discovered their systems were no longer able to reboot.

It seems that Apple and the Symantec-owned PGP suffered a near-fatal failure to communicate that 10.6.5 ships with a new EFI booter that was incompatible with the encryption software’s boot guard. As a result, the update rendered Macs using WDE as little more than expensive paperweights.

“PGP you DO HAVE A FREAKING DEVELOPERS LICENCE FOR APPLE RIGHT???” one outraged user vented here. “YOU CANNOT TEST SYSTEM RELEASES IN ADVANCE???”

A fix was provided yesterday morning by PGP, the details are here:

Mac PGP WDE customers should not apply the recent Mac OS X 10.6.5 update

UPDATE: H security also talks about the same problem.