mannnnnuu dockhals Try removing the Downloads folder inside Documents > Electronic Arts > The Sims 3. Download a fresh copy of Roaring Heights, which will create a new Downloads folder, and see whether the launcher works properly.
The files in Downloads are no longer needed after you install the content they contain, so you could delete this entire folder if you wanted. But if you've downloaded other content that you'd like to be able to use in the future without tracking it down again, you can keep this folder somewhere else and add back the files you want to reinstall when necessary.
Uninstalling and reinstalling the game doesn't help with this kind of issue because it doesn't touch the user files: everything in Documents > Electronic Arts > The Sims 3.
dockhals If the above doesn't help, please let me know whether your computer runs Windows or macOS, for future reference.