Dear DrJamie,
Looks like it might be the problem with the HDD itself and most probably "bad blocks" on the disks (partition D).
I would strongly advice you to SLAVE the drive to another machine with PGP Desktop installed and trying to get access to the disk.
Check if after connecting the drive you will see PGP pop up window to unlocking device and get access to it.
If not try to use pgpwde command line to unlock the disk manualy so:
Start > run > cmd
for x64 bits:
C:\Program Files (x86)\PGP Corporation\PGP Desktop>
for x32 bits:
C:\Program Files\PGP Corporation\PGP Desktop>
pgpwde --auth --disk 1 -p "passphrase"
or
pgpwde --auth --disk 1 --ap "passphrse"
or
pgpwde --auth --disk 1 --wdrt "whole disk recovery taken from the SEMS server"
(provide the password which you tried before with Recovery disk to see if you can successfully authenticate to any of the above commands. Dik 1 is the connected disk presuming disk 0 is your first disk. WDRT can be used only if you had a PGP with server installed not Standalone ).
Try to verify if there are any other users which you can use to get access to the disk so:
pgpwde --list-users
If you don't have another machine with PGP Desktop you should try to get access to the disk with the WinPE disk: (this is more time consuming process as requires to prepare a WinPE disk but as you stated that you had a PGP v10.0.0 you can downlad winpe and burn on CD from below link)
Windows PE & BartPE Tools for PGP Desktop 10.0.x and 10.1.x
http://www.symantec.com/docs/TECH149634
Create a Windows PE Disk for Drive Encryption Recovery
http://www.symantec.com/docs/TECH149477
Once you have got a WinPE CD boot it up and follow below KB (or the commands mentioned before) to authenticate to the disk and copy over the data to another machine). You will have to with WinPE connect another non encrypted dirve to be able to copy data accross.
PGP WDE Recovery using a Windows PE Disk
http://www.symantec.com/docs/TECH149478
HTH