Okay, so, I got my DStwo cart and a non-upgraded 3DS. I copy the "_dstwo" folder over to the microSD card to install the latest OS version, and put it in the 3DS to boot it up. Icon comes up, looks like I'm gold... and then when I launch it, it comes up with an error telling me to please shut the system down and consult the operation manual. Oh fuck you, 3DS...
Experimentally tried many times with different things, such as with/without a patch already added, with/without the "ds2boot.dat" file, reformating the card to be an empty FAT one before copying the OS back over, but nothing seemed to work. I then tried it on my older DS, whose bottom touchscreen no longer works and isn't worth repairing, and find that the card works just fine on the regular DS. It's just the 3DS that doesn't like it, for some reason.
Am I doing something wrong here?