UPDATE
I would like to thank everyone who offered some more solutions to this issue:
meetme2theriver,
abstract_pixels, and
engram_au. I decided to go ahead and re-build the neighbourhood in question. It will take a while, but I hope to be more careful with this one.
******************
Sunday night was the last night during which I played my custom neighbourhood. Fast-forward to Monday morning right up until now, and it just won't show up.
I don't think this file (it's an N006 neighbourhood) is corrupt; and it is the ONLY one which doesn't show up.
I have go-ogled a number of tutorials on this and tried about 20 different "Recover missing hoods" tutorials, all to no avail.
I was wondering if anyone knew of a new and updated tutorial which works.
(It will be a pain for me to have to start all over again)
My game runs on a Windows 7 Home Edition Operating System, over 500GB worth of storage and has a quad core system (or something like that, not really a PC guru). Graphics card will be an Intel i3 core.
And this neighbourhood isn't corrupt. Everything is still intact, it's just unrecognizable by my game, apparently. I have all EP's and SP's, but play without the Pets EP.
Any assistance will be great!