Error: "The on-access driver could not check device control for volume \Device\CdRom0."

I receive the following error in my Enterprise Console regarding one of my Win-7 desktops:

The link to the error does not provide me with any information, just a patch update discussing some changes made to the error codes.

I believe this is related to the Anti-virus failing to scan the CD-ROM drive.  It seems to happen every time a Sophos policy update is pushed to (or pulled from) the desktop.  I am new to Sophos, so I am not sure if this is expected or not.  I could not find any references to this on the Internet or in this forum.

Has anyone got any advise on debugging this?  Is there another log that might provide a better explination?