Air Conditioning - Dripping from ceiling air diffusers

My A/C system ductwork is in my attic--above the insulation. When weather gets cold (Pennsylvania) a few of the diffusers on longer runs start to drip. I assume the moisture rises in the duct and then condenses and drips to floor. Problem is that on way it tends to damage ceiling. Any body know a way to correct this problem? I have removed some diffusers and stuffed the ducts, but it seems there should be a proper solution.

have you gone up into the attic and check the ductwork to make sure they are not exposed to the cold temps? They all should be wrapped/covered in insulation..

The ductwork is exposed to cold temp. The A/C ductwork is the flexible insulated type so it is like a plastic tube surrounded by a wire spring and covered with insulation and a final plastic wrap. The attic it is installed is probably 25 degrees colder than the living area below. I know that the warm air is rising into the duct and then condensing. I was wondering if there is a soluion to the moisture dripping and destroying the ceiling around the diffuser. The system is not used in the winter so I close the dampers in the diffusers and pull the return filter and put a plastic bag around it and re-install it. Trying to block air from rising into system. Was wondering if there is some knid of moisture trap available.

I think you might want to buy a humidity/temp instrument at Radio shack and measure the humidity level in the house. I've never heard of anyone getting this in winter, always the summer time but if your running a humidifier in the house this is plausable...or are you reintroducing the dryer vent exhaust into the living space (some people think they conserve energy this way)...

If all the ducts are insulated. The registers must have insulation installed on top of the them. I have seen the top of the register is cold while the part in the space is warm and it sweats. I will need more info but this can be fixed.

Pete