I've done that multiple times, found numerous Fire Emblem GBA roms, yet the patch will just not work with OpenEmu. I have had this problem with Pokemon Vega and the English translation of Genealogy of The Holy War and the way I got around it was finding an already patched rom and just using that. Another time I wanted to try a pokemon hack called Rocket Adventures made from FireRed, and for that I needed a VERY specific rom in order for that to work. The Fire Emblem GBA rom worked for The Last Promise, so it must be a very specific rom in order for it to work. I have used other UPS patches with multipatch and those have worked, so all I'm left with is that I need a VERY specific Fire Emblem GBA rom in order to work. Anything from emuparadise that I have gotten to work with other patches won't work with this, so I'm running very low on options.