Hi, samiam144. The URL you linked Gateway Ultra with from this thread: http://gbatemp.net/threads/tutorial-installing-rxtools-custom-firmware-3ds-and-2ds.390867/ is no longer seemed valid. Even going directly to Gateway's webpage no longer gives the file. Can you make an upload of this needed file in MEGA for use with the method in your thread?
The link to Gateway Ultra? I linked a google search only, it's against the rules to link the actual files here. The files are still up, I just checked. Search "gateway 3ds" in Google and it will come up.
