I'm also having problems with Fowarder3-DS. I keep trying to make a CIA of a homebrew game (NDS_TGM), and even with renaming the file it keeps refusing to make a CIA (It's for the SD Card BTW). If it does require a certain 64bit version of a executable or something (I have a W7 64bit), then IDK where to find it.
EDIT: Tried with a MKDS demo, and it doesn't work either (The only time when it says Success is when I leave the TID untouched, but of course because the TID is incorrect, it's ignored). Also I have downloaded a 64bit build of make_cia and STILL refuses to make CIA fowarders. Any help?