The error message “Unable to open serial port” is not a Dynamic C error message. The error occurs because the correct port connected to your product is not open, or the serial port you selected is in use by another application. Try closing all other applications using this serial port.
The error “Failed to open the serial interface” means that the correct communication connection has not been selected in the projects. Go to Options -> Project Options -> Communication tab and select the correct Serial Port under Serial Options.
Try a different cable
I have found that sometimes using an old USB cable leads to the board not being connected correctly. It would be in a bad mood if it worked sometimes, but not for others. Using a new or even a different cable solved the problem.
Try a different USB port
The next suggestion is to use a different USB port – sometimes the USB port does not work correctly for some strange reason.
Make sure the connector does not open / unplug the cable
Sometimes the “Unable to open serial port” message may appear when the port is already open. To fix this problem, users suggest disconnecting the cable from another device and trying to reconnect.
This is a simple workaround, but several users reported that it worked for them. Just try them.
Stop Windows Fax and Scan Service
- Press the Windows Key + R keyboard shortcut to open the Run dialog box.
- Type services.msc and press Enter or click OK.
- When Services window opens, locate Windows Fax and Scan service and double-click it to open its properties.
- If this service is not available, change the settings for the fax service.
- Set the Startup Type to Manual and click the Stop button to stop the service. Now click Apply and OK to save your changes.
Several users reported that the serial port message does not open when trying to use the serial port. It turns out the problem was with Windows Fax and Scan.
To fix this problem, all you need to do is stop the Windows Fax and Scan service. Then check if the problem persists.
Please note that this is only a workaround. Therefore, you may have to repeat this every time you want to use the serial port on your PC.