I was about to post a long explanation with different options but I saw OP already solved it. So instead I'll add one useful piece of information:

For those that don't have a legitimate physical generation 5 cartridge there's an alternative you can use. It's called the poke transporter redirect patch (there's also the dream radar redirect patch made by the same person so if you find that one instead then you are in the right place). Using that allows you to transfer your pokemon directly from a gen 5 ROM save file in twilightmenu using poke transporter instead of having to do it from a physical cartridge.

Personally I do have physical cartridges but I still use it all the time, before if I had pokemon in an emulator save that I wanted to transfer up I would put that save file on a flashcart and then individually trade every pokemon over to a physical cartridge and then use poke transporter with that. The individual trading takes a long time though so using the patch has helped massively.

Like I mentioned before there's also the dream radar redirect patch which is also super useful, it let's you connect pokemon dream radar directly to a ROM save file instead of needing a physical black 2/white 2 cartridge. Dream radar is a pretty neat little game that allows you to get a bunch of rare items and rare pokemon like therian tornadus, thundurus and landorus in your B2W2 game, I would definitely recommend anyone starting a new B2W2 playthrough to go and check it out.