Hi Mosq,
If you don't have a backup of your data, please try to slave the drive to another machine with PGP to check if you can get access and authenticate to the disk to copy all your important files/folders. If you manage to do this step and got access to your date and drive I would try to decrypt the drive via GUI or command line from the other machine.
You can use the below KB article - section 2 trying to decrypt the drive from command line on slaved drive
Drive Encryption Diagnosis and Recovery - Symantec Drive Encryption & PGP Whole Disk Encryption
http://www.symantec.com/business/support/index?page=content&id=TECH149679
If decryption is still not possible on the slaved drive you can try to retrieve a bootg.iso from this corrupted HDD which should be by default in C:\Program Files\PGP Corporation\PGP Desktop\ and burn on CD.
Use this CD only as the last resort option of recovery process to decrypt the drive. This is also written in section 3 of above link.
HTH