I have seen this happen twice before. In both instances it 'broke in' after some charging cycles, but in the meantime check this:
Inspect the slot in the receiver and see if there is anywhere specific that there is a nick or burr that the charging handle shuttle may be catching on, or if there is and area at about the midpoint of the slot where the finish has a nick in it. Also inspect the charging handle shuttle (especially where it passes through the slot in the receiver) to see if it has a sharp edge or burr that might be 'biting' into the receiver.
Make sure when charging you aren't pulling at a wierd angle (like trying to rotate it like a doorknob instead of pull back or pressing down really hard) and pull back in one smooth motion.
You can apply a little grease or graphite to the slot too, it won't harm anything.
Shoot me a PM and we'll get it figured out.
Sven