A support ticket, ie email support.
Email me (firstname.lastname@example.org) or post/PM a Dropbox or Google Drive link, etc, for your save there.
At least with the disk version, alt-tabbing out of the game and back can shift NPC/character locations slightly, which in some circumstances could get them into or through a wall (or other obstruction).
Getting a summoning doll to spawn on the opposite side of a wall (armory trick in act 1
), having it enter the battlefields and then returning will place your characters on the other side (or in acts 2 and 3 you can use the teleporter pyramids). The ghost might be targetable from the opposite side.