can't open COM3: [...] cannot access the file because it is being used.

On Windows XP and using Arduino 1.6.0, trying to upload anything to Arduino uno, I'm getting this error: avrdude: ser_open(): can't open device "\\.\COM3": The process cannot access the file because it is being used by another process.

I have the board set to Arduino uno, the port to COM3 (the only one) and the programmer to Arduino as ISP. Infact, no matter what programmer I choose, I keep getting that error.

I'm pretty sure I programmed to very same board a few years ago, but don't remember exactly how, or even if it was using the same version or another (I got also 1.5.8).

Complete message:

         Using Port                    : COM3
         Using Programmer              : arduino
         Overriding Baud Rate          : 115200
avrdude: ser_open(): can't open device "\\.\COM3": The process cannot access the file because it is being used by another process.



avrdude done.  Thank you.

Problem uploading to board.  See http://www.arduino.cc/en/Guide/Troubleshooting#upload for suggestions.