I just made my first attempt at burning a bootloader onto an ATmega328P microcontroller, using an Arduino Uno as ISP. I followed a layout for burning it on a breadboard I found on the internet. It seemed to work fine at first. I swapped the new chip I'd just burned on the Uno board. I tried the blink sketch two or three times, changing the delay times, and it worked. The next time I tried to upload a sketch change, I got this error message:
avrdude: ser_open(): can't open device "\.\COM3": Access is denied.
I swapped that chip out and put the original back in, and it worked fine again. I've just started out playing around with the Arduino and have absolutely no experience with this at all. It would be greatly appreciated if somebody could possibly point me in the right direction to solve this. Seems to be just slightly above my (retired) pay grade!