Problem flashing Walkera QRx350

I am having a problem flashing my QRx350 PRO with APM Planner 2 , when I try to flash the flight controller I get " Unable to gain access to boot loader". I tried it with my Ardupilot clone, and it loaded no problem. The only difference between the two is the bawd rates are different. I also tried it with Mission Planner, but the screen froze up at the same point. Any suggestions would be appreciated.