I personally do not have this error message as all my saves load properly and I am not sure about this one that I am referring to. I had a similar problem three years ago in my laptop, while I tried to save a game that was in Sunset Valley but I didn't know if there was an Error 12. It just wouldn't stop saving. It loaded properly but when I installed Island Paradise in July 2013 I had experienced a crash to desktop when the loading bar was at almost 20%. And when I reloaded it again in September 2013, it loaded properly but later on I experienced some sort of issues with multi-selected portraits. Before re-loading that saved game in Sunset Valley, made backups of it in an external drive, deleted all the pictures of the FeaturedItems folder and set the specific folder to read-only in order for me to avoid crashes.
But when I saved in Roaring Heights, it took more than an hour to save. Knowing that I'd experience Error 12 for the very first time. After that my game had stopped working with a crash to desktop. After that I deleted the .bad folder and my game is now reverted to a previous save. (Referring to this specific one, not Sunset Valley)
It loaded properly before the corruption. And best thing about this saved game is that I didn't travel to any exotic destination (Like France, China or Egypt) or send one specific Sim to University. If I got the whole family to travel and stored tents in any chest I would get this blank house thumbnail problem.
Otherwise I can try starting a new game in Roaring Heights with the Capp family and save before I make changes to the house/members of the family. But if the family thumbnail in the Main Menu turns into a house and the house thumbnail staying as it was, what do I do? Do I get the Serious Error message or the game loads properly?