The USB-host port on the Mega ADK won't work with the version 2.0 library from circuits@home.
Hence the version 2.0 of the PTPcamera-libswon't work either because they rely upon them.
You can use version one of the USB-host-lib on the mega ADK but even this one suffers sometime
from the dreaded "Failed to assert..."-error and might need fixing.
Just do a search on the forum to know what I mean...