volCAMERA contains custom qualifiers, you probably have edited them and clicked OK. Press Ctrl+Shift when you click the EDIT button in the Qualifiers property, you'll be prompted if you want to reset them. Answer Yes and then save the MFA, it will be loadable by old versions of Fusion. I've just tested.

Also not sure how true it is or not, but I hear 2.5+ .mfas won't load in standard 2.5 even if they don't use any 2.5+ features?
Not true, they can be loaded with old versions if they don't use custom qualifiers, child events, or qualifiers in global events or behaviors.