I bought (on disc) the Sims 3 and the Pets expansion. My Pets disc has been giving me problems so a friend suggested I switch to use Origin. Once I did, it immediately recognized that I already own the base Sims 3 game. I redeemed the item code for Pets. When I hit Play, it pulls up that launcher but still asks that there be a disc inserted. "Disc Authentication Error" it says.
The whole reason I made the switch in the first place was to avoid some bugs. For example, about half the time I would open the game, a "Disc Authentication Error" message or something similar shows up (after it's almost entirely loaded) which only gives me the option to close the game entirely. Beyond that, about a quarter of my playing time is cut short because it freezes entirely and, again, I am forced to close the game.