@Annarata I think downloads from The Sims Store are launcher specific; and different TS3 installment have different launchers. Trying to install an item downloaded through one kind of installment specific launcher; into the launcher for another, is one reason for that error message, as well the 'brown box' icons for the items.
It seems to be a generic message though, and can also mean your game is not updated for instance.
Did you download directly from the store, for instance from your Purchase history; and did you open the launcher before you pressed "Download"?
Or did you copy your previously made backups of store items and pasted them into the Sims 3 folder? If the latter: were the previously downloaded items from a different install version?
Do you now have different installed versions of TS3 on your computer(s); through discs, Steam, Origin?
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