I'm assuming you have a PAL game? If so, I've yet to see someone make burned Wii Fit+ PAL work - That error is what most people are getting with it. The NTSC version works fine, at least in my experience.
Did you download the game or dump yourself? If you downloaded it, I have a feeling that the ISO available online is a bad dump. Others with Wii Fit+ issues on here also all downloaded the PAL one.
EDIT: Saw your second post...My friend just burned it and ran with neogamma, nothing special needed (beyond a balance board). I have it on USB loader. Don't know anyone with CORP to try it. You do need CORP for anything to run from system menu.