Savedatafiler does not work in Gateway classic mode.
I have been trying to solve this problem for weeks now, and so far my findings are:
The only way to back up a Pokemon OR/AS save file is to dump the ROM with the Gateway menu. There is no possible way to get the same back onto the cartridge either, at this moment in time.
The only other option is to wait for Powersaves to begin support for the game. I just tried it then, still giving me unsupported game error.
Also it is noteworthy to mention that I have tried using savedatafiler with the so called "4.5 CFW" to extract an OR/AS save, to no avail.
I think the save has to be created inside system menu less than 6.0.0 to be accessible by savedatafiler in the so called "4.5 CFW" which isn't possible for Pokemon OR/AS, as it requires higher than that version to run.
EDIT: I think perhaps because my action reply powersaves is EU and my game is US, it is not working.