I don't know ArchiCad, are the walls just normal lines? In which case I would be looking at layers (on /off), scaling for dashed lines etc, or colours that make the lines vanish. I assume that they don't show on the screen and in plotting? Are the line types supported in LT2024, if you can convert them to continuous lines on layer 0 to see if they show up then?
If the lines show up OK...