Ice means a leak for sure. Is it coming from the actual back of the regulator or is it leaking from a connection somewhere on the regulator and its building up ice on that part of the regulator?
The first time I set my reg up everything was fine and worked for the first day, and I assumed everything was nice and tight. The next day I had a leak and ice build up, and it was because I didn't have the reg to the CO2 tank connection tight enough. Made it tighter, and the leak went away. Be careful not to over tighten connections.