Thank you guys for all the info.
@AndreeAndree: I have posted your link on the first post.
@zerobandwidth: Thanks for all those points you made. I'll try compiling some of it.
I also would like to explain to you guys that this issue has actually nothing to do with Late Night. The first I saw people getting stuck in beds was shortly after the game came out. Must have been August 09. I tested a game for someone who had the problem and there was nothing I was able to do about it except tell the person to start a new game. I also came across a thread in this forum that was from back in '09 describing the very same problem. So this issue has been around forever. It's just the more EPs you add, the more info gets added to your Sims. This is particularly true for WA that introduced the 'MiniSims'. Those are the sims that you see gray in your relationship panel and that are striped of info to only keep the minimum necessary. There are many things wrong with them and the first invisible Sims appeared when you got back from vacation traveling. Twallan has found that most of these invisible Sims have corrupt outfits which makes them invisible in the first place. That can be corrected with the fix invisible Sims interaction in DebugEnabler but since this rerolls everything you might end up with Sims that look very different then they did before.
Late Night with all it's new Sims and that bad routing place in the mountains just added to the problem, making it show up for a lot of people and thus making it a common problem. The more data gets accumulated the likelier you get this bug.
I find it very curious that it seems that once you had this problem, it seems to affect every new game you start, making the error come back a lot earlier. Twallan's Mods do seem to help tremendously for they are constantly cleaning up hung references, broken outfits and temporary items that don't get deleted properly.
If it really is a routing issue, I'm wondering if Twoftmama's Route Fix mod (formerly Richdre's RouteFix Mod) will also help with it.
If you are into mods, it's worth a try as well as Twallan's ErrorTrap (that is core).
That's it for now. Keep posting :)
