[shep]

I think this has to do installing NetBSD to a hard drive that previously used a gpt based boot loader.

The partition table scan identifies the MBR as being MBR-only and GPT data as being present. This is the definition of the problem. (If the MBR is MBR-only and the GPT is damaged, the problem also exists; however, in this case something else may have overwritten some of the non-MBR GPT data, and using GPT fdisk to correct the problem can damage whatever overwrote the GPT data—perhaps a boot loader or disk encryption tool. Proceed with caution in such cases!)

Having identified the problem, gdisk asks what to do. Since gdisk is a GPT tool, it will convert the MBR to GPT form, use the GPT data, or create a blank GPT. Since this page is about wiping out errant GPT data, I'll assume you don't want to keep that data. (If you do want to keep the GPT data, you should select option 2, make any changes you want, and then use the w menu option to save your data. The program will then generate a fresh protective MBR. Do not do this if your MBR data are correct, though!)

If you want to keep the MBR and wipe the GPT, your answer to this question of what data to use is irrelevant. You can then proceed to use the z ("zap" GPT data) option on the experts' menu:

If you have

PartedMagic
SystemRescueCd
RIPLinuX

you can use the gdisk tool to remove the gpt sectors as described here.

As an aside, this is needed for OpenBSD if your hard drive previously was loaded with FreeBSD 9.1+ Debian 7+ and other OS's that now utilize a gpt boot loader.