COM Access is denied

Hi! I have an Arduino Duemilanove and I want to use it in Windows 7. I already install the latest FTDI drivers, and the arduino appears as a USB serial port in the device manager. When I try to upload code to the arduino always says the following:

avrdude: ser_open(): can't open device "\.\COM3": Access is denied.

I already try to change the COM port number and the same happens again and again.

Any suggestion?


My Win7Pro and IDE 1.0.6 shows Serial port COM3 when NO board is connected to my laptop. When I connect my Duemilanove, or an more typically an FTDI Basic type module with a custom board, the laptop makes the boop-beep sound and another COM port appears.

I feel your frustration, but have nothing to offer, except maybe backing up to IDE 1.0.6. I have not ventured into 1.6.x territory yet. No need with '328P, '1284Ps, and 2560s as the chips I generally use.

Hi!! thanks for the quick reply. I already installed IDE 1.0.6 and a I got the same result: “Serial port COM3 already in use”. I also tried with the IDE 1.0.5 with the same result.

Any other suggestion?

Thanks in advance!

Have you disabled your antivirus? Some antiviruses will block communication to ports.

Also be sure to check inside the Device Manage to confirm that you are using the correct port.

I disabled de artivitus (Avast) and I got the same.

I am thinking if my arduino duemilanove really works!

What is about the access rights to the COM port? Are you as Administator? Or, some other application takes the port automatically (like antivirus). Investigate this!
BTW: I am recommendig to use 1.0.6 for now (agree with CrossRoads).

Hi !! thanks for the suggestions.

I checked my windows user and it is administrator. Also, I execute the Arduino IDE as administrator, an I have the same result. Even, I installed IDE 1.0.6 and the most recent FTDI drivers in another PC and I got the same error message.

I am going to investigate about the applications that open the COM ports, thanks for the advice.

I am thinking if my arduino is original or a clone, how can I know that?


Compare the photo here on website with your device and it should be clear. Or provide a picture and people here on the forum recognize it at the moment.

Another way: Try to open the COM port with any terminal emulator application or use Arduino IDE terminal. Any input from the keyboard could cause the Rx LED blink.