Users with PGP Whole Disk Encryption may encounter an issue in which their Macs will not boot after updating to Mac OS X 10.6.5. This is caused by the fact that Mac OS X 10.6.5 overwrites a boot file created by the PGP software (which the tool uses to force authentication during booting) with one that does not allow booting when PGP Whole Disk is present.
Fix
This issue can be resolved by following the instructions directly from PGP; specifically, the steps of “Recovering from Boot Issues with Encrypted Disks.”
These instructions require your Mac OS X installation disc and use of the Terminal.