If you mean that you have trouble picking single notes on those strings, I suspect that you are positioning your hand in a way that forces you to bend your wrist at an awkward angle in order to reach those strings. You should not have to bend your wrist at all to position your pick hand. Position your pick hand by changing the angle of your arm at your elbow and shoulder. The pick action should be achieved by rotating your fore-arm, not by bending your wrist.

I may not have explained this well. Its the sort of thing that is a lot easier to demonstrate than to describe. If it doesn't make sense to you, post again and I'll see if I can really confuse you. ;)