I was having the same issue and resolved it myself.
First: I have an (OSEPP UNO r3 PLUS). It's an Arduino Uno REV 3 made by OSEPP.
I just bought an OSEPP Motor and Servo controller shield. I just got motors working and then I stumbled upon the same error. avrdude: stk500_recv(): programmer is not responding.
I guess while it was connected it made/assigned a new serial port. Found in the Arduino program under menu Tools → Serial Port. I just reselected the one related to the Arduino Uno and bam, problem resolved.