A couple of things to try: Check your collision polygons, use a box instead of the default collision polygon. This can cause lots of oddities... also check your frame rate and movement speed, etc... frame loss can lead to clipping into and through objects especially when not using a fixed shape for a collsion poligon.
I can't download the capx as I don't want to create an account on Speedy Share. You may want to start using dropbox if you want others to download your CAPX since most people use it already for previewing their apps...