toedder: g11 is a GnuBg-generated MET that has values created using rollouts for scores up to 11-away, 11-away. g11 is the default MET for that version. I think the latest GnuBg uses, the Rockwell-Kazaross MET.
Yes, METs are only for match play.
It's very curious that you have this error and I don't have it in versions either side of yours. That's assuming that I'm putting in the corretc position. Perhaps you could upload the match somewhere?
Alternatively, the problem may simply go away if you download and install the latest version.