Cannot place tiles under plates in LDD despite there being room

[Thetford]

I'm relatively new to LDD and I amcurrently designing a building in LDD, and I am facing an issue with tiles. The building incorporates both "modular" and "city" build styles, so both the floors and the back walls can be removed and reattached with ease. This uses tiles under the back walls so that the back wall can be slid out without having to remove the floors (so it can be optionally backless like a "City" building). This of course brings me into conflict with the LDD restriction that prevents anything being placed on tiles or other smooth surfaces despite nothing physically or geometrically actually preventing it. Anyway, I just removed the tiles that would be under the back wall, place the back wall on the SNOT bricks, then replace all the tiles under the back wall. While this worked fine for the ground floor, the first floor only allowed half the tiles to be replaced, despite being enough room underneath. I cannot understand what is blocking the tiles from being there.

First floor without back wall.

Mechanism for attaching back wall on to the rest of the building

Tiles removed in preparation (2 White 1x1, 2 White 1x4, 4 White 1x8, 6 Dark Orange 1x2)

Back wall attached, and all possible tiles replaced, with the remaining invalid (4 White 1x8, 1 Dark Orange 1x2) note how the dark orange tile is invalid despite its mirror image on the other side of the building is valid despite having the same bricks above and below.

Gap under wall with all tiles removed.

I have tried removing the plates at the bottom of the wall and adding them back after the tiles, but it is still an issue over the same tiles. Some tiles go over multiple bricks, and under multiple bricks, is that the issue? Or do I have to temporarily add a more permanent connection between the back wall? I'm at a loss at what do. I have searched, but found nothing particularly relevant.

Also, unrelated, as you may have noticed in some pictures, for some reason the windows can't close. I'm aware the model of frame is outdated, however I use it because I can have both a pane and window frames so I can have glazed windows, yet neither option of lattice window available in LDD fits in the frame.

[Gnac]

Looks like the back wall is "out of system" due to the connection between the 1x1 technic brick and the 87087. If you make this connection with real bricks, you will see a ridiculously tiny vertical offset, which is still enough to give LDD grief.

You can get around this by removing either the 1x1 technic bricks or the 87087s, placing the wall, then replacing the removed parts. Be careful not to build around connections like these, because everything else will be misaligned. It may be easier to find another method altogether.

Edited September 13, 2014 by Gnac

[Thetford]

Thanks for responding. Yeah, I have just noticed a small drop at the top of the wall that wasn't visible at the bottom. Would the vertical offset be enough to throw off a physical model if it were to be made? The only others methods I can think of is two technic bricks and a friction piece, which may be too secure, or the back of the snot piece with the indent (the lantern piece?)

[Gnac]

I myself have built models that way, by abusing the ability to put the offending pieces in later, and it didn't appear to affect the looks or strength in the physical model. I switched to another method though, just because I was worried about the possibility of a hollow stud gradually getting looser from being in a tight hole. This also results in some very tight connections, and may make it tricky to remove the wall for display. Using friction pins sounds like a much better idea. I hadn't considered that!

[Calabar]

The only others methods I can think of is two technic bricks and a friction piece, which may be too secure, or the back of the snot piece with the indent (the lantern piece?)

Using two technic bricks would surely be a more correct design.

About the excessive friction, you could use half pins.