We have found on our Dell Latitude E6500 and 6510 laptops that are encrypted with PGP have an issue with a particular Windows Update. Update KB2393802 seems to be the culprit.
The blue screen occurs after PGP Bootguard authentication. To work around this, boot the computer into Safemode. Go to Control Panel>Add/Remove Programs>check the box to show Windows Updates. Look for the update KB2393802 and uninstall it. Reboot and the computer should now boot without blue screening.