You, most likely, can climb the ladder, it's just that the sweet spot is very small. I remember way back when...It took me a long time to find the place that would activate the ladder climbing. Think I just randomly hit the action button while rapidly walking back and forth under the ladder...until it finally caught.
Now...if it had been the Yuffie lever trap thing... I could give you an answer. For some reason if you manuver Cloud to the front of Yuffie when she starts to cry... and talk to her from her front. The activation of the lever gets reversed.... To activate the lever Cloud's back must be facing the lever. I had a cow figuring that out, as well....was stuck there for about 40 minutes, trying to deactivate Yuffie's cage trap.