After Testing this many times.. and having to deal with the annoying stuck spinning upload wheel that NEVER goes away, having to Force the game to End Rask in Task Manager, this is 100% related to photos taken by your Sims on the Lot. As someone who loves capturing the growing memories of my Sims in photos around their homes after many attempts to find the sweet spot, its right around 4MB that the Game will allow you to upload a given lot to the Community Gallery. I'm not sure how much past that 4MB total it could go, since we dont see a more specific total as is. I just start moving photos I want to go along into a room that gets uploaded with only them to help free up space and give people the option of downloading them to their game. You can still upload with some though until you hit that limit. So I'll usually move them into that room and only upload to my own Gallery until I see that number and then upload it to the Community. Hopefully this helps. If someone from the Sims Team is reading this, please give us some kind of color-coded Red text that alerts us the lot is over this limit so we dont have to Force Quit the entire game everytime.