Seems this is fixed
I got the same bug. Very annoying and it happens freqently.
I just builded a 2 story house, painted it, did the exterior added roofs, windows and doors. But when I moved to do the interior, i could not place walls/rooms or paint the existing ones. This bug happens just as frenquent on a house with a 2nd or a 3rd floor.
I found out that if you remove the roof, u can edit wall again.
Hiya, I have also had this problem, especially when a half-gabled roof section has been placed on the level and is intersecting with the room. For example when placing a roof on a porch of the 2nd level and trying to draw a wall in a room near that roof section, the curser will be colored red and the game will come back with the error "wall doesn't exist" and it will not place your walls. However, I have found a work around.
WORK AROUND for WALL DOESN'T EXIST bug
remove/move the roof section that is interacting with this level
draw your wall/s
replace the roof section
I hope this helps!
-Kulthero777
