Can't download apartment from gallery

shrtnswt  From what you've said, I think you are trying to download an existing apartment that was placed in the Gallery as a room and insert it into a residential rental.  If that is the case, it won't work.  

You can place downloaded rooms from the Gallery and use them in a residential rental though, but you have to do it in a roundabout way.  First, the building cannot be owned.  You'll have to sell it and move all tenants out.  Then, you need to enter the lot in build mode from the map and change the venue of the lot to a residential venue.  Then download the room and place it in the build.  Once you have it placed, then change the venue to residential rental and set all the rooms to define the apartment within the build.  Then you can go back to live mode and have a sim buy the building again and play on.  

Hope this helps.