You have probably set the collission wrong. Go to the database, go to tilesets find the tile you are using for your wall and click on it until it shows an x. I might be wrong since i´m using mv instead of mz, but im pretty sure this is the same across the two versions.
I was listening to songs by Chuck E Cheese's voice actor (Jaret Reddick from Bowling for Soup) when the meds I was taking for my stomach virus apparently stopped working. I can't take my next dose until morning, but it's no use anyway. I'm officially sick again. Of course, I'll definitely take the next dose either way, but it's useless now.