The world does not install for me either. I put it in the Downloads folder, the installer runs, says it was a success installing then DONE and when I check the installed worlds folder, it's not there. I have all expansions and stuff packs.
Saturn, Have you done the steps neccessary to have it in game?
EA made it extra hard for all world creators so any user made world after Seasons is creating that issue. Luckily, workaround is easy and fast.
-Install the world with doubleclick or trough the launcher (which you already did)
-Go to your DCBackup folder, arrange your files by date modified and look for most recent and biggest file there (should be around 129000 kb).
-Rename that file - big coded name rename into Union Cove Seasons, and package into world. You will get notification that will change the function of the file or something in those lines, say yes to that. Thumbnail picture now should look blank.
-Copy that file into
C:/My Documents/Electronic Arts/Sims 3/Installed Worlds (this is where it should go by template)
and into:
C:/Program Files/Electronic Arts/The Sims 3/Base Game/GameData/Shared/NonPackaged/Worlds
(in this folder you'll have at least Sunset Valley in same format)
Sometimes, settings are made that files are not showing extension. If you click on that biggest package to rename it and you don't see xxxxx.package, go to Control Panel - Folder Options - View - unmark the "Hide extensions for known file types". Then continue with the renaming and coping the file in noted folders.
That is it. Now when you start the game Union Cove Seasons is listed among worlds and you can start the game with it.