This article provides information on reasons for the "Unable to Connect to COM Port" error message and how to fix it.

The error message "Unable to connection to COMx" or "Serial Port Access Denied" typically occurs when a program or device cannot access the specified communication port (COM port).

Example screen shot of serial port error.



Here are some common reasons and solutions:

1. Port in Use:

   • Another application might be using the same COM port. Close any other applications that might be accessing the port.

2. Permissions:

   • You might not have the necessary permissions to access the COM port. Ensure you are running the application with administrative privileges.

3. Driver Issues:

   • The driver for the device connected to the COM port might not be installed correctly or might be outdated. Reinstall or update the driver.

4. Port Configuration:

   • The COM port settings might be incorrect. Check the port settings (baud rate, parity, data bits, stop bits) and ensure they match the requirements of the device you're trying to connect to.

5. Hardware Issues:

   • There might be a physical problem with the port or the connected device. Check the physical connections and try using a different cable or port.

6. Conflict with Other Devices:

   • There might be a conflict with other hardware devices using the same resources. Check the Device Manager for any conflicts or issues with the COM port.

7. Software Configuration:

   • The software might be configured incorrectly. Verify the software settings and ensure it is set to use the correct COM port.

If after checking the above you are still getting an error, you may consider performing a factory reset on the device. Please refer to your product's User's Manual for help with this.