Did you manage to sort this?, I just did the same to a V1.10 E300, tried to update to V6.10 & got checksum error..!, probably due to lack of storage in EEPROM, you would think the loader would check for this.
I was hoping reloading the original version would do it but since thats what you tried it doesn't look good, do you have a copy of the v1.2 ?, if so any chance you could post?.
One thing that springs to mind is to check the eeprom or flash memory size and possibly replace with larger but if you can't get the original system file to work I doubt that would help!, I will let you know if I have any luck.
I just recovered the E300 by loading the v1.12 system into the terminal, I got it off my original Mac_Programmer+ CD, does the terminal go into sysload when you press (backspace + F1) at power up?
I just recovered the E300 by loading the v1.12 system into the terminal, I got it off my original Mac_Programmer+ CD, does the terminal go into sysload when you press (backspace + F1) at power up?