I'm actually the person who got this error. I suspended the game in world 2-1 of this mappack
, and quit the game. When I opened it again, I selected the default SMB mappack, and the option to load the save was still there. When I selected that, I got the error in the screenshot, and the save was gone.
I'm running Mari0 version 1.6 on a Mac, OS X version 10.8.2.