It sounds like you might be using a coffee that is too oily. What kind of coffee are you using? If it's an oily roast, trying switching out for something a little drier. Also you might want to try cleaning and calibrating your machine. Here's an instructional video on how to do that: http://www.wholelattelove.com/videos.cfm?playvidID=339. Also, I suggest rinsing your brew group really well, and then letting it dry overnight on a dish rack.