Unable to Connect RFD900x2 to Mission Planner : “Access Denied to COM6”

Hi all,

I’ve been trying to connect my RFD900x2 radio to Mission Planner without success. Here’s what I’ve tried so far:

  • Reinstalled Mission Planner
  • Reinstalled all relevant drivers
  • Closed all other applications that might be using the same COM port
  • Reflashed firmware on both the local and remote radios

I can read and write the radio settings without any issues, and the radios are recognized correctly. The problem only occurs when I try to connect in Mission Planner.

The error message I get is

Åtkomst till porten COM6 nekades. (“Access denied to port COM6”)

vid System.IO.Ports.InternalResources.WinIOError(Int32 errorCode, String str)
vid System.IO.Ports.SerialStream..ctor(String portName, Int32 baudRate, Parity parity, Int32 dataBits, StopBits stopBits, Int32 readTimeout, Int32 writeTimeout, Handshake handshake, Boolean dtrEnable, Boolean rtsEnable, Boolean discardNull, Byte parityReplace)
vid System.IO.Ports.SerialPort.Open()
vid MissionPlanner.Comms.WinSerialPort.Open() i C:\Users\mich1\Desktop\CubePilot\MissionPlanner\ExtLibs\Comms\CommsSerialPort.cs:rad 510
vid MissionPlanner.Comms.SerialPort.Open() i C:\Users\mich1\Desktop\CubePilot\MissionPlanner\ExtLibs\Comms\CommsSerialPort.cs:rad 148
vid MissionPlanner.MAVLinkInterface.OpenBg(IProgressReporterDialogue PRsender, Boolean getparams) i C:\Users\mich1\Desktop\CubePilot\MissionPlanner\ExtLibs\ArduPilot\Mavlink\MAVLinkInterface.cs:rad 886
vid MissionPlanner.Controls.ProgressReporterDialogue.RunBackgroundOperation(Object o) i C:\Users\mich1\Desktop\CubePilot\MissionPlanner\ExtLibs\Controls\ProgressReporterDialogue.cs:rad 111

Also worth noting: I can connect to the radios using RFD Tools without any issues, so the hardware and drivers seem to be working.

Has anyone experienced this? What might I have missed? Any suggestions would be greatly appreciated!

Thanks in advance.


I have a feeling that if you are in the RFD settings page in mission planner that the relevant COM port then becomes “claimed” and can’t be used for telemetry connection. When you close and re-open mission planner, can you attempt to connect to com6 without first going into the rfd page?

Try using the RFDTools