@seishir0_0
Are you on Mac or PC? Are you using any mods that affect build mode (like BBB) and are you using build CC?
Is the lot a game lot that you are modifying, a lot you built from scratch yourself, or a lot that you downloaded and are modifying? Also, what is the lot size - 30x20, 40x30 etc.?
Is it crashing when trying to draw walls on just that lot or does it happen on every lot in that save? You've already said that it doesn't happen in other saves, so it seems to be save specific rather than the game itself.
If it is happening on other lots, have you built, modified or placed any other downloaded lots? A problem like this can be caused by something that happened earlier and you are just finding it now. And if you have downloaded lots and installed them anywhere in your game, especially since For Rent was released, there have been a lot of issues with lots in the Gallery being glitched. You might have gotten one of those and it is affecting build as well as lots that were uploaded with CC you don't have when you install it, can cause all kinds of issues.
When did the problem start? By that I mean, did it start after Lovestruck released or before? And if it was before, can you remember if it started around the time any of the earlier packs were released like For Rent or Horse Ranch?
If you'll please answer the questions above, it will be really helpful to me so I can help you further.
Hope this helps.