The upload tool could not open the serial port, so no data ever reached the board. The two messages after the port name tell you which fault you have: “the system cannot find the file specified” means the port is gone, “access is denied” means something else is holding it.
What the message means
Windows names the port, for example COM3. avrdude asks Windows to open it. If the board is unplugged or the cable carries no data, the port does not exist. If another program has it open, Windows refuses the second request.
Fix it in this order
- Read the last words of the message. “Cannot find the file specified” points to cable, driver or the wrong port. “Access is denied” points to another program.
- Close the Serial Monitor, other IDE windows, PuTTY, Python scripts and any robot dashboard that opens the same port.
- Unplug the board, wait three seconds, plug it back in and reselect the port under Tools > Port.
- Open Device Manager > Ports. If the board shows with a yellow mark, reinstall its driver. If it does not show at all, change the cable.
- Move the cable to a rear motherboard port or a different port, without a hub.
If you see this, do this
| You see | Do this |
|---|---|
| The port number changes after every replug | Normal with some clones. Reselect the port each time. |
| It works after a reboot only | Another program grabs the port at start-up. Find it in Task Manager. |
| Access denied with nothing else open | A background serial tool is running. Check the system tray. |
Related
programmer is not responding, Arduino IDE setup.
Last reviewed: November 2026. These are the usual causes and the order that finds them fastest. Test on your own board; clones and cables differ.