Have anyone seen such a behavior? On a beach lot with several sims, just one suddenly cannot move in unlevelled terrain typical for beaches. It happens randomly after having been ok for months. I noticed it to happen when 2 sims use the same path to go somewhere and meet in opposite directions. Most of the time it is OK but all of sudden one of them stop and cannot go anywhere any longer. They just stop with a thinking bubble like there's something on the way and they cannot go thru. I didn't find a way to correct this error either by "Reset" or using FFS debugger to throw errors.
It also doesn't cause any error in Test Cheat Enabled.
The only solution I found up now, is to move them out to another lot. Sometimes deleting the sim and recovering it again also helps. Not always.
The strange for me is that Only One presents this behavior where all the others are all right.

I've honestly never seen this before. Can we assume that you've done the entire game problem FAQ? Does the problem occur in a vanilla (no cc at all) game, with a newly generated save game? From what you say, it sounds like it's just this one neighborhood.

Did you try using the Stuck Object Remover from MATY?

When you say "Only One presents this behavior where all the others are all right", do you mean just this one lot or just this one sim? If it's just this lot, the lot may be corrupted. You could always move your sims out and delete the lot. If it's just this sim, that's a more serious problem since sims cannot be as easily deleted, and the damage that a corrupted sim causes to your neighborhood is harder to remove.

Well, I cannot play "Vanilla" because I modified the game to my taste and this implies modification in the root of the game that I have no intention to revert. Those modifications are not corruptions to the game, it is just to avoid that some features that puts me mad continues to happen. I tested them for years and years and I Do Not post them for other users. A reinstall for me, is a piece of crazy work.
2) It is not One hood, it can happen wherever and in lots that were played without any problem and beach lots without any kind of extra modification. With extra modification I mean I did not change size, shape or anything in the lot. I just build a very normal house and move in a family.
3) It is not One Sim, it can be whoever, no matter gender and no special features. By special features I mean, I do not use vampires, witches, plantsims, zombies, the only creature I use is the BigFoot because he is not romantic and can be funny sometimes. Bigfoot created with SimWardrobe object. Up now it didn't happen to children, toddlers or babies. Most of the time only Adults.
3) The Stuck Object Remover - if you mean a yellow box that delete invisible things in live mode, I place dozens of them in the place and in live mode it says that 0 objects have been removed.
4) I always move the families out of their lots regularly because I know that lots get corrupted by the game self. None of my families live in the same house for more than 2 generations and I started to create a lot in the Uni hood specially to work as cemetery, so I move all the deads to that lot and when someone wishes to be scared I invite it over there. So, it is not the reason for the corruption. What makes me wonder is that such behavior can happen even after a recent move in.
5) FFS debugger - Pescado's tool, I always use this tool when I see something that is not looking very normal. It has no effect in this case.
6) Hood Check - Mootilda's tool, I use it regularly and the only thing that is registered is some sims that have a memory of meeting himself. It always repeat the same thing and I sincerely don't know why. None of my sims seems to have a memory of meeting themselves in game.
7) Test Cheat Enabled True - I always play at least 30 minutes with this cheat On if I suspect something is wrong. No errors were thrown in this case.

Finally - All my hoods last for years without any kind of problem. So yes, the smallest problem makes me look for a definitive solution.

At this time, I don't know how to help you. I hope that someone else will have some ideas. If I think of something later, I'll post. Good luck!

I had a similar problem and I found it to be associated with maybesomethingidunno's Surfs Up and Inges portals as described in the download describtion.
June 13th: There seems to be a conflict with Inge's buyable beach portal(s) which causes an error. I promise I will be looking into a solution, ASAP (I've got so much work to do for Real Life at the moment so my progress with this is slow). For the time being, please remove Inge's buyable beach portal before going surfing. If you use the Portal Revealer, make sure the portals have returned to an invisible state before surfing. (Thanks to keef1973 for pointing out this issue.)

I have this issue with children all the time - for some reason they are unable to walk on even the slightest incline. My solution was just to use cheats to give them the ability to teleport (bon voyage required), and then I just had them teleport everywhere instead of "go/run here". This doesn't get to the root of the problem, but it keeps the game moving along.

Keef1973 - Thanks for the information. I do not have this surf thingie installed but I have Inges beach portal. It can have something to do with it because I notice that from hood view I can see dozen of beach towels all over the lot.
It is possible that they are invisible when inside the lot, not sure. This would cause sims to stop because they don't seem to be able to walk over some objects. I'm not sure right now if I still have Inges custom beach towel in my downloads because I noticed some issues before. It is possible that Inge's beach objects cause some conflicts. I don't use them so much, so I could live without them. My doubts are still concerning to non beach lots. I didn't use any of Inge's objects but got the same issues in unlevelled terrains where sims seem to be stopped by something abstract. As they always try to walk in straight line, unlevelled terrains are a big issue because they do not consider alternative paths. But it was a good beginning and I suppose the solution is somewhere in this direction. Have played all sort of relative flat lots and there are no issues at all.
Thanks for the clue.

hmiller. I still didn't get any issue with youngers but teleport them don't solve the issue for me. If you teleport a sim that is trying to go to an specific place and can't reach it, would only place them anywhere else but not avoid that they try to resume the interaction they were intended to. In my case, teleport the faulty sim would only place it in another perspective and if the invisible object is still on the way, it doesn't remove it. If this object is result of a mod conflict, then it is much more serious than a simple placement. Most of my mods now are Object mods and are clearly depending on a visible and present controller. I have to reckeck all mods that are invisible or placed directly on sims and were not made by myself. Thanks.

Problem partially solved. It seems that I build far too difficult houses for the sims low intelligence. I concentrated myself on other non-beach lots where the problem arises now and then, and came to the conclusion that there is no way to make sims aware of complex curves. The only way is to calculate the curves self and place hindrances on strategic places so that sims are forced to contour them using straight lines. It is essential when building rooms inside foundations, a technique I use often. Unlevelled terrain close to the foundations have to be made inaccessible by means of special hindrances that can be even bushes made placeable in slopes.
I removed most of the mentioned object mods and I still can see a lot of beach towels from hood view, so I still don't have the final answer. But the problem is significantly reduced, so far I'm pleased. Thanks all for the help.