@Frostfyre7 I've never seen that error before, but my first thought is that it's misleading, and there might instead be a corrupt file in your user data folder. The fastest test is to move your Sims 3 user data folder out of Documents\Electronic Arts and onto your desktop, open the launcher to create a clean folder, and try to install only Sandy Shoals Sea Shanty. If it works, the issue is in your old user data folder; if it doesn't, it's a problem with the download or the store or similar.
Ther other thing you can try is installing the wave station separately first, as it's the only premium content item in the set. Then try installing the entire set, and if it works, you can uninstall the duplicate wave station. But please try that in a clean folder too, just to keep things simple.
Removing the Documents folder worked!!! Thank you so much, you rock. :D
