WNDR4500v1

Good Evening, 

I've been working over on the dd-wrt forum trying to figure this router out. I have a matching pair of WNDR4500v1's. One of them loaded a .chk copy of dd-wrt effortlessly and works perfectly. The other has been less than great.....

Any attempt, via web gui or nrmpflash, to flash dd-wrt fails. Trying to flash anything other than netgear firmware crashes it (goes to a solid amber power light). I've realized I don't have the right serial cable to serial into this......but what's interesting, I can upgrade or downgrade netgear firmware via the web GUI with no problem. Anyone have recommendations or anything on this?

Thanks