I have never had problems with mold on seeds that are in the soil only in paper towels. The reason I have had mold on seeds is because they were in the paper towels for about a week and were probably too warm so i would assume your soil is too warm, or possibly too cold as I have had mold on my soil when the lights go out and the soil gets too cold. So just make sure your temperature is around room temperature or just a little warmer and it should be fine. If your house is cold put the pot with soil and seed an inch to inch and a half under a cfl, I use the 42 watt, keeps the soil at a good temperature. Thats all I can think of.