JRJ Concrete Walls: Some not showing up

[Julius Caesar]

I have spent quite a lot of time trying to get these to work, and it is probably time to ask for help.  The problem is for me some of the walls appear completely transparent: the only evidence that the lot has been placed is a nice little fence at the top of the slope, and a change in the texture in the road or whatever at the bottom, but nothing on the slope itself.
Lots that work for me:  the transport enabled lots, all lots featuring overhangs (for extending the walls under bridges, etc.
Lots that do not work: the ordinary 1x1 lots, the diagonal lots.

Here is a history of what I have done:
1)  Downloaded and installed the dependencies given on the lex: BSC_Texture_Pack_Vol3 and BSC MEGA Props JRJ Vol06.
2)  Downloaded and installed all the other five BSC JRJ mega prop packs
3)  Downloaded and installed the diagonal walls sets themselves.
4)  Located and studies the relevant tutorial on Simtropolis, although this is quite old and the lots no longer seem to work in quite the way suggested.

A.
I have tried placing the lots, in all possible orientations, in a 15 m deep trench started by the NAM hole digger lots, and in a 15 m trench started using Smoncrie's hole digger lots.  I have tried placing them along the sides of slowly rising trench starting deep and ending shallow, dug by extending a railway line from a 19 m hole.
I have tried using my normal plugin folder, and a plugin folder containing only the walls themselves and the dependencies in 1 above and Smoncrie's hole-digger lots.
In all cases the results are consistent: the overhang and TE lots work and the 1x1 and diagonal lots don't.  This seems to apply for all 5 different wall types, although I did not do a completely exhaustive test.
B
Using a plugin folder containing only these lots and the dependencies in 1) I examined the lots and associated props using SC4PIM.  This is right at the edge of my comfort zone, and I can't guarantee that I have got it right.  Never the less, the results seemed consistent with my observations under A:  the lots that behave properly seem to have associated props in BSC JRJ Prop Pack 6, the others do not.  I also noticed that in  Prop pack 6 there are corner shaped props for the seawalls (which I have not installed) but not for the concrete lots.
C
I have spent quite a bit of time looking through the forums for similar problems, and although there seem to have been some problems with the fences earlier on, no one seems to have had problems with the walls themselves.  This is the opposite of my problem: my fences seem fine, but not the walls. However, there does seem to have been a bit of a reorganization of related material on the lex since the last post in March, so I suppose something might have gone wrong somewhere.

I had similar problems with JRJ's rural and residential walls, but have not studied the situation in the same detail.

So there seem to be three possibilities:
a) I have made some sort of silly mistake (unfortunately not uncommon.)
b) There are some props missing from BSC MEGA Props JRJ Vol06 (and all the other JRJ Prop packs.
c) My computer is funny in some way.  It is a 64 bit HP using an Intel core i7 and running Windows 7.

There is a workaround for straight trenches: I can use the 1x1 lots to get the fences and the overhang lots to put walls under them.  But I can't think of a workaround for the missing diagonal walls.

Any help or suggestions would be much appreciated.

[Swordmaster]

Could you show some pictures of what you see?


Cheers
Willy