Agent running, Arduino Uno detected, com3 access is denied

I can’t upload a sketch to my Arduino but did so yesterday.
coding on the online IDE, I have the agent installed running, reinstalled, paused, quit and opened again. without luck.

same error: avrdude: ser_open(): can’t open device “\.\COM3”: Access is denied.

also worth noting the IDE picks up on the Arduino being disconnected physically as well as the agent turning off. the agent is white when on and greyed out when off.

Would really appreciate any leads helping upload a sketch

Isn’t windows great! Taking a SWAG I would check for some other process using COM3. The first thing is to power down the computer and restart and see if it goes away. If not you can try to change the COM port.

I just had that same issue today - COM port 5, access denied.

After the typical unplug/replug USB, reopen IDE, etc... I started closing programs one at a time, and by chance, this was the first time I had tried uploading while Ultimaker Cura was running simultaneously.

I wasn't connected to my printer, but Cura was simply running. Closing the application immediately solved the problem and I could upload just fine.

Restarting the computer should also work, but in my case, it was helpful to know for the future. Note to self, close Cura when finished.

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Great find, thanks for letting us know.

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