PGPError #-121978862 on Attempt to Encrypt Whole Disk

RECENTLY RESOLVED

PROBLEM:

Running PGP Desktop 10.1.0 (Build 860) on MacOS 10.6.6 on a MacBook Pro, I get PGPError #-121978862 on attempt to encrypt an external whole disk.  The error occurs shortly after the onset of the instrumentation phase.

Can someone please tell me where to look up the meaning of this error?

RESOLUTION:

Have you repartitioned the disk as a GUID drive? (Note - that will destroy all info on it)