My sim games does it also. I have no mods, but the thing is that I am downloading stuff from the Sims 3 Store. When I click download it pops up then says "Unknown Error Occurred" I think I know how it happened (at least mine) it said my World Adventures needed an update, so then I clicked yes then when it was downloading it wasn't responding so I quit it. Nothing happened it didnt ask for another update, but it wouldnt work!! I tried to find a way to fix it. NOTHING WORKS! ☹️((( I have all the expansions so its annoying ☹️((
Can you try downloading and installing the super patch? That should hopefully fix the problem you have. Click the manual patch link in my signature to be taken to the downloads page. You could also delete the ContentPatch folder from Documents > Electronic Arts > The Sims 3 and that will force the Launcher to prompt you to download and install the Store patches again.
