Error when making walls taller

@Wilsoooner Hmmm.... I've never seen that message. I'm assuming that there is something on that floor level, or perhaps the floor level above, that's stationary and can't make the shift upward for some reason. Much of the time when an item is deleted on placement, and sometimes in a shift like that, the game will try to put it into the household inventory rather than completely delete it, if the home is owned.

A few things I would try:

• Save the game before you try this. Now go around the house and remove items that you suspect may be an issue. Just stick them in the yard or household inventory or a basement room if you have no room. Try moving between each item removed and see if you can find the problem item. After you find the problem exit the game without saving (so all of your items will be back where they were when you re-enter the game), then re-enter and fix the problem.
• Did you place any debug items, hidden objects, or enlarged items? If you did, you could try removing them in the manner above and test.
• You could try it with MOO enabled and see if it works then. If it does, turn off MOO, save the lot to the library, then place it on another lot to see what deletes then.
• You could try moving the household out and see if you get the same error message when the lot's unowned. The game just deletes anything that cannot stay where it is when the lot's unowned.
• You can try saving the lot to the library and placing it on another lot and see if the issue remains.
• Do you use Mode or CC? You could try removing them and then deleting the localthumbcache.package file in your 'The Sims 4' folder. 
• If none of the above helps please upload your lot to the gallery then share the name of it here plus share your name in the gallery if it's different than it is here. I could then download it and test in my game.