Seems to mean the box is overheating! Are you keeping it in the oven? 🙂
Anyway, turn it off for 10 minutes, and turn it back on again. If it stays white, you’re done. If it starts off white then goes red after a few minutes then it;'s either genuinely overheating or it’s faulty. If it goes red pretty much immediately then it’s definiitely faulty.
Edit: My answer is based on Virgin Media’s connectbox as it seems to be the same hardware but with better documentation. UPC’s docs don’t mention any red light for the connectbox (although they do for the gigabox or whatever it’s called).