Calibration lost and not able to arm


I am new to this topic and have a Tarot Hexacopter with an Arduino Mega 2560 and an 2,4GHz WiFi receiver.
We followed the tutorials and configured the plane via MissionPlanner (uploaded the files via ArduCopter).
The main problem ist that MissionPlanner looses the calibration of the accelerometer after tthe menu is left (e.g. for switching to flight data). Also, disabling the pre-flight checks do not work, when clicking active/inactive (may be named arm too), we get an error: rejected by MAV. We used the terminal to configure as well and the motor test works fine, but we just cannot arm the engines.

Also, when configuring via Terminal in MissionPlanner and then connecting to use the Flight Data screen, the calibratio of the accelerometer seems lost. We did not do the ECS initialization because we cannot get rid of the rotors, so the Hexacopter would takeoff immediately. Since no autopilot is required and with disabled pre-flight checks, this should not be a problem.
We also followed this: in the MissionPlanners normal GUI.

Could someone help us?

the apm 2560 is no longer supported. and i dont recall the last time i tested any functions for it. i would suggest updating to something like the Cube

Thanks für your answer, I made it work and I cab fly now fine but we cant switch our controller