I'm using an Arduino Uno board with an HP computer running Windows 10 and IDE version 1.6.8. Arduino was working fine for me until a few days ago, when (and I suspect this is the root of the problem) I accidentally tried to upload software with something connected to the RX and TX pins on the board. Now I continually get the error message below:

avrdude: ser_open(): can't open device "\.\COM2": Access is denied.

The only other thing that changed is I disconnected a bluetooth dongle (Kinivo BTD-400 Bluetooth 4.0 USB Adapter for Windows) without uninstalling any software, so I suspect that software may be searching for open COM ports and disrupting the Arduino upload.

I've tried everything I could find about troubleshooting online, including that "did I brick my arduino" post elsewhere on this forum, and nothing has worked or even changed the problem - please help! I believe I've narrowed down the problem to my computer scanning open COM ports, but I can't find any reliable way to make sure that doesn't happen.


  • Have you tried powering down your PC and turning the power-plug in the socket the other way around? This often fixes this issue. (Given you're using AC power)
    – aaa
    Commented Apr 7, 2016 at 11:30

1 Answer 1


It sounds like Windows thinks that port is in use and isn't letting the ArduinoIDE access it. If it's the same port your dongle had been using, try plugging the dongle back in, then dismounting it before you remove it. Hopefully that will clear the port for other uses.

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