OS Windows 7 32 bit
CPU-AMD A8-3850 APU with Radeon(tm) HD Graphics (4 CPUs), ~2.9GHz
GPU-ATI Radeon HD 3600 Series
RAM 4GB

Background" I've been playing TS2 for 12 years and have used multiple layers of subfolders ever since the game started supporting them. Never had a problem until now.
My favorite savegame has been played regularly for most of that time. A couple of months ago I downloaded TS2UC because I was unable to reinstall my game due to my basegame disc becoming damaged. I immediately fired up the new game, enabled CC and quit. Then transferred my old savegames and download folder to the new game. Everything worked fine. I thought. After a few days of play I noticed that random sims were having their instance number changed and losing all their data. After a few weeks of trying to find what was corrupting that one savegame (other old games were not affected) I became frustrated and decided to try something new.

I found the Medieval Charter Challenge and decided to try that. I had nothing in my downloads folder that was appropriate to the theme so I moved the folder to desktop and started a new one. Made all my subfolders in preparation for the new CC and started downloading everything medieval that I could find. Got everything sorted into appropriate subfolders and was ready to start. Part of my downloads was custom sims. Loaded the game and entered CAS. Looked for my custom sims. There they were in the simbin looking just as they appeared on the websites. I chose the first one. WHOA!!. What happened to him? Maxis skin, Maxis eyes, Maxis everything. There were No custom skins or eyes or makeup or clothing available. I left the game and came here and read the page about custom content. I had originally put all the stuff that came with the sims in a folder called SimStuff. I now took that folder and dumped it all into the SavedSims folder. Loaded the game. Everything worked. That was fine for the adults but I wanted genetic children and there was no custom clothing for children. Back out and transferred and assortment of clothing from the Clothing subfolder to SavedSims. NOW I could make my families. Today I placed them on their lots. Ready to build. Nothing in build showed up but walls and floors. Pulled some hair out.

Intermediate steps I have done: When I first had the problem I assumed it was bad content causing it. Pulled most of the new CC except what was needed for the sims, so had nothing in the downloads folder except some of the hacks that I have been using for the last many years. I also renamed the game folder and started a clean game and put my original downloads folder in that. Worked fine. Checked it again today. Worked fine. Renamed that game folder and started another. Put the medieval downloads folder and Saved sims in that. Didn't work. Came here and read more pages. Took out everything but Insim from downloads folder, SavedSims folder and the new neighborhood folder. Started the game, entered Belladonna Cove, made a new sim, put him on a lot and checked to see if insim was showing up. It was not. Hmm, I didn't try taking it out of it's subfolder.

But the point is- why is the game not reading the subfolders now when it has for years and still does for that one game? I have triplechecked to make sure Downloads was spelled the same on all three games. I read somewhere that walls and floors didn't have to be in the downloads folder and I have verified that in my game. Okay, I have done everything that I could think of. I hope someone has some more ideas.

It will only read so far

Have you run the Sims2CleanInstaller to see what it says? It will normally point out file names that are be too long.
UC - never use a cc or registry cleaner to start with. If you had used one, it deletes the .dll files the game needs and you may have to do a repair. You won't lose your cc or your game this way, but may need to reinstall your graphic rules and camera mod.
I have played UC since its release - first on Windows 7 and now, for a while, on 10, without any problems (except one or two due to severe stupidity attacks )
Make sure you have enabled the cc in the game - probably not the problem, but check anyway.
The only other thing you can do is to make all the names of your folders, subfolders and documents shorter. There are a lot of downloads out there with names that are far too long to be read.

@Kankritty - The old game reads Downloads 5 subfolders deep. The new game reads no subfolders at all. I switch from one to the other by renaming the user folders.

@Justpetro - If something had changed in the registry it should affect both games but I haven't used a cleaner since installing UC. It can't be anything in UC or again, it would affect both games. CC is enabled and shows up as long as it is not in a subfolder. My subfolders mostly have one word names: build, buy, clothing, genetics, hacks in first layer. Walls, floors, doors, windows, etc, or casual, sleepwear, undies, etc. in second layer. Third layers might be AF, CM, TF, EM, etc. I have shortened all lengthy file names. But a name as short as NMS-net.package does not show up if placed in a subfolder in the new game. But in the old game this file ' hkw_FA_AAS40drs-bluegray plaid.package' is read with no difficulty. It makes no sense.

Make sure your current folders are named "Downloads" and SavedSims", spelled EXACTLY like that, with the caps and bolded letters in the right place.

It could be an idea to remove the Downloads folder, run Bodyshop, and let the game regenerate a new one. If you just make a folder and rename it "Downloads", the game won't always take to it. It's the same with SavedSims. Weird, I know, but some people have had that problem.

If you want to check if your Downloads folder works at all, put in a furniture object with a custom mesh you know where to find ingame, and a CAS item with a custom mesh you know you can find, plus perhaps a few recolors of the CAS item in SavedSims. Put them directly in the folders, no subfolders. If they show up, the Downloads folder works (just not the subfolders), but if they don't show, there's something wrong with the folder itself.

Also, if you do start a new game, make sure you really have enabled CC for the new game. The setting for this is saved somewhere in the "The Sims 2" folder (possibly the userProps in config?), so if files are moved about a little too much, you might end up deleting or moving out the file with the settings, and thereby accidentally turning off CC. The game is also a bit stupid on that area, so sometimes you have to enable CC more than once for it to stick.

@simmer22 - I think you may have hit on it. I just finished trying the game with a bunch of build stuff and furnishings loose in the Downloads folder. Plus my most essential hacks copied fron the good folder. None of it showed up in the game except walls, floors and fences. Two of the hacks, Insim and Simblender, have always showed up as new meshes but not today. There are a lot of new meshes with the new lots I installed but I checked all categories of objects and there were no new meshes anywhere. I'll give your idea a try and report back in a while.

Sad to say, it didn't work. I removed all the medieval downloads from the game, including the things not in the Downloads folder. Deleted the folder and started Bodyshop. New folder appeared immediately. (Why is that? I've never made anything but clothes and sims in Bodyshop and they always saved to SavedSims) Then I copied a few things from my good Downloads folder into the new one and entered the game. Nothing with a mesh showed up, though recolors did. I decided to try something else. I went back to the original folder, deleted that Downloads folder and copied my original downloads folder from the pre-UC game. (Which is what I had done when I first started playing with UC). Entered game. Everything showed up properly. Hmmm. Now two games work. Went back to medieval game. Did same thing here. Didn't work.. So I moved my neighborhood back to the old game. Ran it, no problems. Added SavedSims folder. Ran it, no problems. Added a road DR and some build materials. Ran it, no problems. I'll continue adding a few things at a time until something stops it.

It just occurred to me. Could a bad lot cause this problem? The first thing I did to begin play was install several medieval lots and then place them in a neighborhood. And when I transferred my downloads to a fresh game I also moved the lots from one lot catalog to the other. They are still in the game that doesn't work.

I will also reinstall CEP - which is needed for Maxis recolors, but I think one is supposed to install it again with a new game.

@Justpetro - Yes, with each new game I copied the ZCEP folder and the GMND.package into their proper places. The MMAT.package remains in the UC folder in Programs where I was instructed to put it. It's the latest version so doesn't need reinstalling. I've never used the auto-installer cause I like to know where things are going.

I really can't see a lot causing this, something odd is going on for sure. All I can think is it's some setting someplace preventing it from reading sub folders. Perhaps you should try reinstalling the UC.

Just so you know - the CEP may need reinstalled on occasion, whether it's the latest version or not. It can be corrupted (dunno how) - I've had that happen to me. Just once, mind you. But it did and I needed to reinstall.