QGroundControl fails to open serial port

I’m using pixracer and UART7 is system console serial port.

I’m trying to connect through this port in QGroundControl.
But, it shows this error message.

I can use nsh by screen and minicom through this port, but I don’t know why I can’t connect though this port in QGroundControl.

I also tried to execute QGroundControl as administrator. But QGroundControl doesn’t permit to execute as adminstrator.

I also executed the following commands to fix this issues.

sudo usermod -a -G dialout $USER
sudo apt-get remove modemmanager

But, it also fails.
Does anyone can tell me what is problem?

Did you solve this problem. I have the same problem when I try to connect pixhawk telem2 to qgroundcontrol, but I doesn’t have this problem when I try to connect with micro-usb port.