I just got my Phantom 2 back from DJI who replaced the 2.4 receiver. I can't calibrate: keep getting yellow flashes. When connected to the Assistant, it will not show "GPS Mode", but defaults to "Normal Flying". Now when I switch to Naza Mode, I get one green + three red flashes when calibrating, and when connected to the Assistant, it will show GPS Mode. Whatever it's doing, the thing is very unstable and will drift in almost every direction (yaw, pitch, altitude). I am very new to this, but have read the manual thoroughly, read a lot of forums, and I'm impatient. Any help is much appreciated.