I fixed this problem for me. Here's how I did it: Go to this link and try the solution on there, but I only paid attention the the 2nd paragraph by the user "rosemow". Link: http://forums.thesims.com/en_US/discussion/836387/cant-save-lots-to-library-or-upload-lots-and-sims-to-gallery
Once you've done that, whatever Sim/Household/Lot you're trying to upload to the Gallery, open in up, in CAS/in-game, and save a new version of it. That new version should be able to be uploaded to the Gallery. Afterwards, when you go into your Library, delete the older version. I hope this works for you!
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