I swear I have searched this forum under every possible terminology I could think of pertaining to this issue. I've seen a few similar problems, but thus far have not seen any definitive solutions, at least for my particular problem. Pardon the rambling...
Most likely user error (my fault!). I was happily playing along when I decided to have one of my original sims pay my current house a visit. I had played her with no problems just days before. I was confused when I didn't see her name, so I checked her husband's relationship panel. She was gone. I checked her childrens' panels, and still she was gone. In the family tree, she has no thumbnail next to her husband's. In the husband's memories, she is called "subject" (kissed "subject" for the first time, got married to "subject", etc). In SimPe, her ID number (0x017B) is there, and I can see her memories are intact, under her ID number in "family ties", all her relationships are there. All her family members have her listed as 0x017B unknown. Her name and picture are not there. I do backups frequently, so I put in a backup folder,went into the game and packaged her. I exited the game and switched back to my current neighborhood, (several interesting events had occured since that backup and I didn't want to lose them) and installed her. When I played the game, I saw she has all her memories, but does not relate them to the sims they pertain to in game. I didn't realize copies of all her relationships were also added to the game. So, I went into SimPE and manually changed all the family ties to the current sims, replaced "subject" with her name in all the other sims' memories, and the game seemed restored, a few quirks were there, like her adult children not recognizing her as their mother, but after some more SimPE editing, that was fixed. I played for hours last night! This morning, when I went to the neighborhood ("Pleasantville" is the one I play), all the lots and houses were gone! Sims were still in the sim bin, and SimPE was showing the characters were in the game, but I couldn't get to them because there were no houses. So I made things worse somehow. I decided to play the backup game, deciding to give up on the current one. The lots were gone there, too, even after pasting them into the lots folder. I reinstalled and I was able to find Jennie (the original problem sim) in the backup game, and my lots and houses were back. However, Jennie was lying on the ground like an infant, and nobody could interact with her. Even more disturbing was that certain family members were whistling (that attraction thing) about a particular romance sim who was their neice, granddaughter, daughter, or sister! My game is a mess now, duplicate sims are showing in the sim bin, and if I delete one, both files get deleted. What I would like to do is change the 0x017B sim and all its files back to Jennie. Or create a new Jennie, and transfer her character to the "unknown" sim file (which is really her!) Is there anyway I can do that? I'm in way in over my head here, now, and even my trusty backups are giving me problems. Again, excuse the long post, it's just such a mess! And if this should be in another category, I apologize.

I'm so frustrated! :swear:

I should also mention that I do have several hacks in the game: JT's teen pregnancy mod, Insiminator 1.5, Inge Jones' teleporter shrub, phone/taxi hack, no cheering, homeworksometimesfasterfun,daily gardener, no cops and robbers, no dancing with strangers, many more from here, but none have given me trouble before. I don't know if I may have messed up by hack abuse...

I believe the cliché "you can't get too much of a good thing" is incorrect. You tried to make everything perfect and look at the mess you are in! If I was in your place I would reinstall the game and play it without hacks.

I've had sims disappear out of neighborhoods after messing around in SimPE. I can't really put my finger on what the cause was, but it might be best, if you can, to just go back to the neighborhood save where your sim still existed, even though you might miss out on the stuff that happened after that.

I have a lot of those hacks too, and doubt that they are the cause of your problems, but I could be wrong.