Alas! Patience did not work. I left it for about 30 minutes, and even after the "Saving" icon (and the music you mentioned) were gone, the screen was still black, with the little watch cursor! Anyone experiencing the same thing?
Ok, my Sim made another random Gnome of Invention yesterday, so I immediately tried to sell it at the Consignment Store, but it didn't appear in my "consignable" inventory, even though I was able to sell successfully the widgets that were also there. Did some kind of patch/update cancel the ability to sell these, perhaps?…