RI is Respiratory Infection, I don't have any personal experience of it in my collection (touch wood it stays that way) but it is essentially a snake cold. Look for mucus around the nose and mouth, bubbles from the nostrils and whistling when breathing. As far as I'm aware it is caused when conditions aren't quite right for the species in question, so first port of call I guess would be to adjust the temp and humidity so they are correct, ensure the enclosure is clean and get the snake to a vet. Like I say, I have yet to have to deal with this myself, so hopefully someone more experienced will reply to your post. These are the first steps I would take though.
Al