Look at the flashprom details from the manufacturers (should be Amtel IIRC) but you should be able to short pins 23, or 24 to ground or maybe both (it has been a few years, please check the speck sheet) and that will allow you to program in the firmware with Fpro as long as the flashprom is good. I have used this method several times to get past errors or PassPort firmware. You normally don't have to go this far for just the MPT firmware, that will overwrite with FPU. Worst case is you replace the falshprom and start from scratch, but could be a few hours with a service monitor.
do you happen to have a picture or some other reference on how to do this reset, i have also flashed the wrong firmware to my radio and have gotten the error and it will not allow me to go back and reflash the correct firmware.