yea, i am thinking that something else must be wrong with it. I can successfully overwrite the bootloader with a clean image provided by the arduino ide.
even after i do that though, it gives the same error. no matter if i try the UartSB way, or the way your blog post shows.
the only way i can get it to write to the rainbowduino is to compile it in the IDE then use avrdude commands to upload the sketch.
i am using an seeeduino with avr-isp on it though, so the limitation may be set by that. but thats only when writing the bootloader. that shouldnt have anything to do with how it writes the sketches does it?
did you guys image your arduino via isp programmer and avrdude? if so do you have the commands that you used?