Check for air flow over the indoor coil first.
New filter, coil not clogged with dust.
After that the next cause is often a low charge.

What are the outside temperatures overnight that you're trying to run this air conditioner in? If it drops into the 60's or there abouts that's your problem right there. Air conditioners simple will not work very well in those ambients without some type of mechanism to keep the head pressure up. And by dropping the setpoint that low that machine is forced to work all night to drop the space down to that temperature. The longer it run the less ineffective it becomes and the more it tends to freeze up. Also if you are trying to cool the inside much below 70 an air conditioner looses it affect. There just isn't enough BTUs to remove. In effect, no load on the evaporator, when you don't have any load on an evaporator you get ice up. More then likely you're just asking to much from your residential air conditioner.

Mr.havac/brickeeye,
Both responses are plausable, shortly after posting, I had a friend come over and check the charge. On the suction side( outside temp at about 82 deg F) and set point in the house at 72 deg F we found the pressure at about 52psi. At this point the split temp was running about 12 degrees. We gave it a charge to get the pressure up to 68psi and the split went up to 15-18 degrees. It was extremely humid that day, so the ideal 20 degree split I think may have been unachievable.
I agree with the concept of diminishing returns when it comes to lower inside temps than 70 degrees and with the loss of head pressure. I had my wife read your response and surprisingly, coming from someone she doesn't personnally know, has agreed to bring the night-time sleeping temperature up a degree or so.

Thanks for your help.