A issue was opened recently for AutoCasperNBI, where 10.11.2 NBI’s generated for not accessible over ARD or VNC.
Some digging revealed this this only affected NBI’s with the “Reduce Image Size” option selected.
NBI’s for 10.7.x – 10.11.1 work fine over ARD or VNC with that option selected, so some investigation was needed. Below is the investigative work, but you can also skip straight to the resolution.