Can't move/delete objects and unpause the game in a specific lot

Heya,

I've restarted the game at least three times now without saving, but every time I place a stair, I can't (re)move it. Not immediately, weirdly enough, but within 5 minutes of playing it happens. The problem also happened with a room, I accidentally moved the floor a bit higher, but when I wanted to lower it, it was not possible. It was also not possible to delete the room or delete separate walls. Trying to close the game with no saving seems to result in freezing, only solution is logging out with help of ctrl-alt-delete. Another problem is that I can't unpause the game anymore after building mode, although this seems to be the case only after the game starts acting up. 

Before starting building yesterday I did notice that all my saved files where gone, apparently I moved a map on my pc. I moved them back and that solved that. I've been building this house for hours yesterday and did not experience any building problems. Saving it was not a problem. However closing it down and saving (I always save twice) was a problem, it froze, so I had to ctrl-alt-delete my pc out of it. But the file was still there. I'm not sure if any of this might have caused this problem. 

My attempts to solve so far:

- Removing all contents of the map 'Mods'
- Restarting and no saving when it happens (at least 5 times now)
- It gave me once an error about some 'generational problem'. Googling this didn't help.
- testing if cheats have anything to do with the errors, doesn't seem to be the case 
- Going back to another house with my family, there are no issues there. The game runs and saves normally, stairs and other objects act normal. If I then go to the 64x64 lot again all the weird issues happen. 

Any ideas how to solve it? I never had this problem before (~200 hours of playing so far)