I was not aware that The Sims 2 hav e a strange limit of number of wall segments when you cannot build more walls… until I built The Condominium.
During building the 6th floor, I encountered the bug, so I had to replan the blocks thinner and simpler, to reach desired height of 7/8 floors.
The limit is 2100 wall segments. Half height walls are NOT counted towards wall limit, BUT you cannot build them once wall limit is reached. Foundation walls and pool walls are counted towards wall limit, BUT… you can add them even over limit.
SOLUTION (trick to exceed wall limit): Delete the foundation, build as many walls as you can, then rebuilt foundation and pool.
In my example, each block’s floor contains 68 pieces of wall (there are no internal walls), so I built 30 floors over the 4 blocks, totaling 2040. With the remained 60 walls I built lift houses on the roof and an entrance porch. Then I rebuilt foundation and pool which bring the number of wall to 2440 segments.