I'm brand new to all this, but learning quickly. This info may be useless to most but there may be a fewas green as myself.
I have a sketch that compiled, and ran fine with an Uno but I couldn't get it to upload to an Adafruit Pro Trinket 5V 16mzFTDI. I had the correct board selected, the correct programmer, and port, but kept getting this error.
avrdude: stk500_disable(): unknown response=0x30
I kept chasing bootloader problems, and trying to make things complicated.
I wasted 2 hours before realizing, the serial print code I used for troubleshooting in my original sketch couldn't be uploaded to a Pro Trinket. Comment it out, no more problem.
Maybe some other rookie will benefit from this, then again, maybe not.