If you stand as close as possible to the wall, surround the character with packages or crates (maybe miscellaneous loot would work?) and summon a summoning doll, you can get it to appear on the opposite side of the wall (
armory trick in act 1). If you then have the summoning doll enter the battlefields, when you exit you will also be over the wall. You might have to enter the battlefields yourself first, to collect barrels and any crates you can find.
Some people have found that alt-tabbing out of the game and back can shift the character positions slightly, which you may be able to use to get through a wall.
It is also possible to change the character positions manually:
Teleporting anywhere (via hex editor).
This problem is most often associated with the first part of act 1; the last section of act 1 opens up a bit, and later acts have more open areas outdoors and less narrow corridors in caves, etc.
Check your messages (click 'My Stuff' in the top menu bar, then 'Messages').