Kinderkraft crib model 710
On the bottom of the front rail that drops (the drop rail), there are two plastic tension pieces (one at either end) that engage the two fixed, bottom rail slider hardware (the long, narrow pieces screwed top-and-bottom into the lower, inside portion of the tall, upright crib ends). These tension pieces are spring loaded, and the outer edge of each one rides along the outside (i.e., the parent's side) of the two bottom metal rail guides. Their purpose is to supply outward pressure against the lower part of the drop rail - that's what you push against when you press your lower leg upon the bottom of the drop side of the crib to lower it. They insure that when up, the drop side locks safely into place. I suspect these tension pieces are your problem. It sounds like they are improperly installed. Good luck.