Well, getting blue mold. Either the spores are freely roaming around or you're encouraging the conditions overmuch.
Try oiling the next cheese you make. I'd suggest an Italian type for that. You could see if it grows it as much.
Also, do your cheeses get blue mold coming back and back or does it slow down at a certain point? I've found that the second to the third or fourth week are when molds attack the most, but if you drive them back they stay away once your rind is good enough.