When I toggle active households I lose all my backpack-inventory and my fridge inventory too. Maybe you could unload all your inventory onto the property-floor/counters and toggle households and then toggle back and see if it's gone.
Spawned babies need your compassion
I like Story Progression; I just need it to make sense.
When my Sim-grandson moved out of the neighborhood:
I have this problem too. One of my Sims has a "skill training" book (for gardening, I believe, purchased at the bookstore) in her inventory. The book is for levels 1-2 in the gardening skill. After purchasing it, she raised (via practice) her skill level beyond this, and now I can't do anything with the book.
If I click on it, the only option is "Read", but it's ghosted out (since she is beyond the level the book applies to). I can't click and drag the book anywhere... not to the "Sell" box, not into the house or onto the bookshelves, nothing.
Unless EA provides a fix, I guess this book isn't going anywhere for the foreseeable future? I'm just glad our Sim inventories don't seem to have an (unreasonably small) limit on the number of items they can carry.
At least it's not a perishable item, like some of you have gotten stuck with!