I had this same problem yesterday with my world, but I noticed that the eraser tool was "glitching" and cloning onto some other images, so out of curiosity I went back and deleted + replaced those and then the world was able to upload. Basically try deleting any images you think may be "glitched". I recommend backing up the Sokpop folder under AppData/LocalLow beforehand in case something goes wrong.
Or, like someone else said, it might resolve on its own. It could just be some server issue. I hope it works for you!