I was just out with my 501, kept getting a "Calibrate Horizontal Gyro" but it would go away and and the LED's were flashing the proper sequence so I'd fly it, flew ok but drifted and it had some control issues, I did the full re-calibrate as the guy in the video did, thing fly's great now, stays right in place if I let up on the sticks, return home, follow me, everything,
Start by binding the transmitter & quad, then proceed, if the compass calibrate message doesn't come up try standing the quad on it's end and move it around, when the LED's go to red flash then calibrate compass and next the Horizontal gyro.