I was trying to add a beach property to my Twikkii Island, but it would only let me add an unbuilt 3x5 site. The one I was trying to add wouldn't turn green, but stayed on red. I moved a house around that was already on the beach and tried to put the pre-built property where it was, but it still wouldn't work. What am I doing wrong? Shouldn't I be able to add a property?

Beach lots are buggy little prima donnas. They don't like to be swung around and they will only place on slops exactly the same as they were built on and if they do by chance place in an area they are not 100% happy with they may crash your game. So it's better if it doesn't place. With the pre-built property you need to know what beach it was built on and make sure you are trying to place it on the same beach. You can't build on Twikkii Island and then move it to Blue Water. And even if conditions are all accounted for you may still be out of luck. That's just the chance you have to put up with if you download or build and save a beach lot.

Thanks joandsarah! I seem to remember from playing before that the vacay lots were tricky!

Be sure to backup your save game before installing a beach lot. Because they have such a tendency to crash your game, you'll be glad that you can just restore from your backup.

The LotAdjuster (see my profile) can help you with crashing lots by adjusting the lot edges to match the neighborhood terrain. However, there's no guarantee that the lot will look right with different lot edges.