This question has probably been asked a trillion times before, but here goes anyways.
After toying around with tutorial files I got on the forum and so forth, I still can't figure out how to make my guy jump through platforms (yeah, I'm probably a moron). I've only been able to get the extremes. Either he jumps through the bottom 4/5ths of the platform but then cant go past the top fifth almost like hitting a ceiling, or my character jumps through successfully, but on his way down to touch the top of the platform, he stands for only a microsecond and then suddenly drops back down. It seems like I've step-by-step copied another project file that had it working fine and it won't work.