Hi, this is a bug in mtxcontrol I think, when you are using a new rainbowduino it has FF in all the EEPROM bytes so mtxcontrol tries to load 255 frames and crashes. The fix is to add a line in mtxcontrol’s firmware.pde:
void load_from_eeprom(word addr) {
word num_frames = EEPROM.read(addr++);
if (num_frames > 10) return; // uninitialized eeprom