I've grown Aglaonema's for a long time but I've never seen this happen. Sometimes curling leaves can be caused by a virus. It's really hard to say from a photo though what the problem might be. Do you have a botanical garden in your area where maybe you could inquire of a master gardener who might be able to take a look at your plant in person to diagnose the issue, or possibly ask a local nurseryman?
You could post this on our Aroid Forum too, we have some very knowledgeable folks over there who'd be familiar with this type of plant and may be able to offer suggestions:
http://garden.org/forums/view/...
