I couldn't connect the APM 2.6 to mission planner. I don't know where the mistake is ? I downloaded the latest version of Mission Planner and plugged the APM 2.6 to the PC then I chose "Install Firmware" and firmware was installed. Next, I chose the "APM Copter v3.3.3 Hexa". When the process bar is done, I cliked to the connect button located right-hand top of the Mission Planner. It was almost done but it failed as giving the error that " You cannot load new firmware while connected via MAVLink. Please press the disconnect button at top right to end the current MAVLink session and enable the firmware loading screen". Then,of course, I disconnected it and searched for the enabling the firmware loading screen but i couldnt understand what the meaning of it is. Can you help me about it?