Quick layer question

[siderus]

Can anyone help with this one. I get jobs from Architechural firms drawn on many layers. Something I run into is this. I will click on a line for example and it will say it is on a certsin layer lets say WALLS. So I turn off the WALLS layer and the line is still there. Can it be on 2 different layers at once and if so is there a way to find out what others it is on.
Thanx

[Lazer]

maybe there is a line under the line so when you turn of the line by layer your still left with another line

If you turn of a layer then all lines on that layer will turn off aswell
the line you see must be on a different layer or on layer 0