NDD "Error on Hard Disk 2" - which HD is that?

Running Norton SystemWorks 2009 Premier Edition 12.0.1; Norton Utilities 22.0.0.52 on Win XP Pro.

 

I am trying to diagnose possible failures in a USB-attached HD, which reported some problems earlier. When starting Norton Disk Doctor, I get the error, "Error on Hard Disk 2 - Master Partition Table is Unreadable."

 

I would click "Yes" to repair, but my main HD is a GPT disk, and I of course do not want my main HD bricked. How do I really know what is "Hard Disk 2"?  Is it the same numbering scheme as in Win XP Disk Management? Does NDD understand GPT disks?  Thanks for any assistance.