Greetings, I assume the remote you have for your D600 that you are using is the ML-L3? The D600 has an IR receiver built into both the front and the rear of the camera body. Try replacing your ML-L3 remote battery with a fresh one. It is possible your battery on the remote is low and not providing enough IR output? Also please note there is an IR receiver built into the rear of the D600 body in the lower right corner. The dual front and back IR receivers for the D600 are very convenient in different shooting situations and the ML-L3 remote is relatively inexpensive. In the D600 shooting menu, the remote control option allows you to program how your ML-L3 remote functions when its shutter release button is pressed. (page 85 of the D600 manual) Good luck.