Thank you nikkipollard, Jeffin90620, murray dickinson and Torfinn for further replies and your good help!
nikkipollard: Yes, the dwg save for the same file that is messed up as dxf I can open again in TC 2015 and the walls are still walls and everything looks right. Further, my tiny CAD viewer app displays everything nicely as well, whereas the walls are simply not there when the dxf file is viewed!
Jeffin90620: Fine, I did attach 2 files are you can see in my post above; but the images do not appear directly in the post, just the links. I shall attach again in this post and follow your directions to see what happens.
It is clear that for my current version of TurboCAD and usage of same, I must backup using dwg files. They work very well.
EDIT: aha! with the attachments, the png file shows directly in the post but not the pdf, which is what I attached previously.