Sims can only purchase unowned businesses or unoccupied residential lots?

I wouldn't think it's a bug per se. In RL you can't just buy another person's property, unless they are willing to sell. If there are no unowned businesses or property you need to either move the Sims, or evict them to make the lot owner-free and available for purchase.

"Bronwin2;d-959406" wrote:
I get this error message whenever I try to buy a restaurant. Is this a bug? I can work around it by buying an empty lot and either building a restaurant or store or placing a pre-built one, but I can't buy one directly. What's up with this?

Was the restaurant previously owned by a now deceased sim? Because that can cause this. The only way I know to solve it if it is the case is to track down the household and play them just long enough to have them sell the restaurant so you can buy it.