I've made other changes since I got it working, but I think that the problem was:
+Afterburner Energy: default
;Position: (575, 735)
+Weapon Energy: default
;Position: (850, 735)
I deleted "default" from those lines - that fixed it. Then I started playing around with moving the HUD elements around and found a couple of HUD configs I liked elsewhere on this forum.
If it helps, I bought FS2 on Steam, installed it and then used the auto installer (it's a .jar) to install everything else so that's the config file that came down with the latest downloader.
I'm running in 1920x1080 by the way.